Abstract The findings on depression and anxiety among brain tumor patients have so far been based on case series and case samples. In Finland, psychiatric research in relation to psychiatric symptoms among patients with different types of brain tumors is lacking. The study population of this thesis consisted of 101 patients (39 males and 62 females) aged between 20 and 82 years with a solitary primary brain tumor treated surgically at the Oulu Clinic for Neurosurgery, Oulu University Hospital between February 1990 and March 1992. The major histological subgroup consisted of gliomas (40%), and the rest were meningiomas (33%), acoustic neurinomas (13%), pituitary adenomas (8%) and other types (6%). The psychiatric symptoms of the patients were assessed at three time points, namely before tumor operation as well as at three months and at one year after operation by two valid measurement instruments, the Beck Depression Inventory and the Crown Crisp Experiential Index. In addition, the patients' functional state was evaluated by the Karnofsky Performance Scale and their quality of life according to Sintonen 15 D. Prevalence of at least mild depression before tumor operation was 30% for males and 38% for females. The mean depressive scores decreased significantly for up to one-year during follow-up for both males and females, but they remained notably high in all patients. Decreased functional status (KPS under 70) in the patients was significantly associated with high depressive scores at all measurement points. The decrease in the mean depressive scores was significant among patients with an anterior tumor and those with a pituitary adenoma. Five-year survival of the brain tumor patients was found to be mainly associated with the histology of the tumor. Survival time in months (SD) of the patients with high-grade (III–IV) gliomas was shown to be 22.5 (21.4), while it was 50.2 (19.9) for the patients with low-grade (I–II) gliomas, and 58.2 (9.4) for the rest of the patients. Depression among low-grade glioma patients was significantly associated with worse survival at five years follow-up. The level of anxiety was shown to be significantly higher among patients with a primary brain tumor in the right hemisphere compared to the anxiety scores among patients with left hemispheric tumors. A significant increase was found in the level of obsessionality over time in the female patients with a brain tumor in the left anterior location of the brain at three months after operation. The level of quality of life (QOL) was significantly worse among female brain tumor patients compared to males. Depressive females had significantly lower quality of life compared to that of non-depressive females up to one-year follow-up after surgical operation of the tumor. Depression, anxiety and obsessive-compulsive symptoms have to be recognized and be treated by psychotherapy and pharmacotherapy as soon as possible at every unit where brain tumor patients are followed and encountered.