Objective: To examine the association between psychiatric disorders and neoplasms. Methods: A follow-up study of a population-based cohort of patients admitted for psychiatric care between the ages 13–17 years. The cases were patients with a follow-up diagnosis of neoplasm. The K-SADS-PL interview was used to assess DSM-IV based psychiatric diagnoses at adolescence. The treatment episodes due to neoplasms and related psychiatric disorders were extracted from the National Health Care Registers. Results: Of the original cohort, 6.3% of subjects had a neoplasm diagnosis. Male cases were characterized as taking snuff and females as having a fear of becoming obese. 75% of cases had smoked regularly and 47% suffered from substance misuse disorder already in adolescence. At a mean age of 22 years, the diagnoses of skin or soft tissue neoplasms were prevailing, three being malignant neoplasms of the skin, mouth or colon. Non-psychotic disorders were comorbid both two years before (26%) and after (33%) the neoplasm diagnosis. Conclusion: Focus on psychiatric symptoms of patients with neoplasms may enhance their treatment outcome and quality of life.