Medication management constitutes a large part of registered nurses' (RNs) daily work in municipal elderly care. They are responsible for monitoring multimorbid older persons with extensive treatments, and they often work alone, without daily access to physicians. RNs’ drug monitoring is, in this thesis, based on the concept of pharmacovigilance. Pharmacovigilance is about the science and the activities that aim to improve patient care and safety in drug use, that is, to detect, assess, understand and prevent drug-related problems. The overall aim was to explore conditions for pharmacovigilance from a nursing perspective, focusing on implications of RNs’ competence and use of a computerized decision support system (CDSS). Both quantitative and qualitative research methods were used, including a questionnaire (I), focus group discussions (II), individual interviews (III) and an intervention study (IV). In total 216 RNs and 54 older persons participated from 13 special accommodations, located in three different regions. RNs who had completed further training in pharmacovigilance rated their medication competence higher than those who had not. However, there was no difference between groups in the number of pharmacovigilant activities they performed in clinical practice (I). The RNs appeared to act as “vigilant intermediaries” in drug treatment. They depended on the nursing staff's observations of drug-related problems. The RNs continuously controlled the work of staff and physicians, and attempted to compensate for shortcomings in competence, accessibility and continuity (II). RNs’ use of a CDSS was found to affect drug monitoring, including aspects of time, responsibility, standardization of the work, as well as access to knowledge and opportunities for evidence-based care (III). The CDSS detected significantly more drug-related problems when conducting medication reviews, than the RNs did. Nevertheless, this did not result in any significant improvement in the quality of drug use in the follow up, three and six months later (IV). This thesis contributes to the recognition of pharmacovigilance from a nursing perspective. Increased medication competence seems to be insufficient to generate pharmacovigilant activities. RNs depend on other health care professionals and organizational conditions in order to perform their work. A CDSS has the potential to support RNs, both in structured medication reviews and in daily clinical practice. Inter-professional collaboration is crucial, with or without a CDSS, and the entire team needs to be aware of and take responsibility. Other important conditions is the existence of well-functioning communication channels, competence across the team, and established procedures based on current guidelines.