The aim was to psychometrically test the S-HSOPSC and HSOPSC, investigate health care staff’s perceptions of patient safety culture and their suggestions for improvement. Methods: A three-time cross-sectional study with data from health care staff (N= 3721) in a Swedish county council was conducted in 2009 (N = 1,023), 2011 (N = 1,228) and 2013 (N =1,470) using the S-HSOPSC (I, II, III). Health care staff’s suggestions for improvement were analyzed in a qualitative content analysis study (IV). Results: The S-HSOPSC (14 dimensions, 51 items) is acceptable for measuring patient safety culture (I). Health care staff held a positive attitude towards their own unit’s teamwork, and a less favorable attitude towards hospital managers’ support for patient safety work (I). Managers held a more positive attitude towards patient safety than others and enrolled nurses held a more positive attitude than registered nurses and physicians (II, III). Positive attitudes towards learning, nonpunitive response and staffing was associated with positive attitudes towards overall safety (II). Health care staff’s attitudes towards patient safety decreased between 2009- 2013 for 12 dimensions (III). A diversity of approaches, nuanced in relation to the informant’s profession was suggested to improve patient safety, for example ‘Increased staffing’ ‘Teamwork and collaboration’ and ‘Committed management' (IV). Conclusions: The S-HSOPSC is suitable for measuring patient safety culture. Supporting and committed managers, teamwork and collaboration are important for patient safety improvement. RNs have an important coordinating position in patient safety work, since they work in close proximity to the patients, and strategically in teams, where decisions of importance for patient safety are made. Health care staff attitudes towards communication, nonpunitive approach, feedback and learning from mistakes have deteriorated. To prevent from organizational fatigue, actions are needed. / Baksidestext: In health care, many patients are being harmed, with leads to suffering and financial costs. Health care staff’s patient safety culture reflects their attitudes towards safety for patients. The overall aim was to psychometrically test the questionnaires S-HSOPSC and HSOPSC for measuring patient safety culture, investigate health care staff’s perceptions of patient safety culture and their suggestions for improvement. In this thesis, respondents in the most common health care staff groups participated. Health care staff held a positive attitude towards patient safety culture within their own unit’s work. The perception of patient safety culture differed between professions and managers had a more positive attitude towards patient safety culture than others. Health care staff’s attitudes towards patient safety decreased during the measurement period for almost all aspects and they suggested many approaches to improve patient safety. Patient safety needs to be a responsibility for everyone. Supporting, committed managers, teamwork and collaboration are important for patient safety improvement. RNs have an important coordinating position in patient safety work. / Syftet var att psykometriskt testa frågeformulären S-HSOPSC och HSOPSC och undersöka sjukvårdspersonals attityder till patientsäkerhet samt förslag till förbättringar. Metod: Tre tvärsnittsundersökningar genomfördes. Sjukhuspersonal (N = 3 721) i ett landsting besvarade enkäten Hospital Survey on Patient Safety Culture om patientsäkerhetskultur år 2009 (n = 1 023), 2011 (n = 1 228) och 2013 (n = 1 470) (I, II, III). Sjukvårdspersonalens förslag på förbättring av patientsäkerhet studerades med kvalitativ innehållsanalys (IV). Resultatet visade att den svenska versionen S-HSOPSC (14 dimensioner, 51 frågor) är acceptabel för att mäta patientsäkerhetskultur (I). Sjukvårdspersonalen hade en positiv attityd till aspekter av patientsäkerhet som handlade om arbete på den egna vårdenheten, men en mindre positiv attityd till högsta ledningens stöd för patientsäkerhetsarbetet (I). Chefer hade en mer positiv attityd till patientsäkerhet än andra och undersköterskor hade en mer positiv attityd än sjuksköterskor och läkare (II, III). Förmågan att dra lärdom av misstag, en icke-skuldbeläggande attityd vid misstag samt bemanning var positivt associerad till en positiv attityd till generell patientsäkerhet (II). Sjukvårdspersonalens attityder till patientsäkerheten försämrades under mätperioden för 12 av 14 dimensioner. (III). Sjukvårdspersonalen föreslog en mängd förbättringar av patientsäkerheten. Förslagen var nyanserade i relation till informanternas egen profession (IV). Konklusioner: Engagerade chefer är viktigt för patientsäkerheten. Teamwork och förståelse för varandras arbete är gynnsamt för patientsäkerheten. Sjuksköterskor är viktiga i patientsäkerhetsarbetet, då de både arbetar nära patienterna och i team där beslut fattas som rör patientsäkerheten. Personalens attityd till kommunikation, icke- bestraffande synsätt, återkoppling och lärande i samband med misstag har försämrats. Detta kan indikera en organisatorisk utmattning och kräver åtgärder.