Objective: The aim of this review was to identify the most important risk factors for postpartum depression.Background: As a visiting student for three weeks in a Norwegian psychiatric hospital I met a deeply depressed mother who had given birth to twins a couple of months earlier. I instantly got inspired to learn more about postpartum depression and especially risk factors for this condition.Method: Using the search terms “postpartum depression”, “risk factors”, “etiology” and ”prevention” MEDLINE and PsycINFO databases were screened in order to find studies examining risk factors for postpartum depression. Studies that focused particularly on risk factors and/or prevention were chosen. The results from those articles that were judged to have the right focus were then critically assessed and organized in nine groups according to topic.Results: The following nine groups of risk factors were identified; psychopathological factors, sociodemographic factors, reproductive factors, social support, relationship (especially to partner), life events, somatic illness, obstetric factors and circumstances related to the baby itself. Conclusions: Psychopathological factors were found to be risk factors: past history of depression, depression during pregnancy, other previous psychopathology, anxious personality features, anxiety during pregnancy, “postpartum blues” as well as psychiatric illness in relatives. Other risk factors were low socioeconomic status, unplanned/unwanted pregnancy, pregnancy complications, poor social support, relationship problems and traumatic life events. The results showed that psychosocial risk factors were very important. Several other possible risk factors for postpartum depression were found, but further investigations are needed for replication and extension.