A study sample of 51 patients with acute and transient psychotic disorder (ATPD) (ICD-10) is presented. The findings suggest that, in hospital settings, ATPD is a non-frequent condition with onset in early adult life and most often associated with female sex, good premorbid social functioning and no or minor/moderate psychosocial stressors. The DSM-IV criteria distribute the patients into three diagnostic categories: schizophreniform disorder (41%), brief psychotic disorder (33%) and psychotic disorder not otherwise classified (25%). A high prevalence (63%) of personality disorders (PD) is revealed after recovery from the psychotic episode. The ATPD is not related to any specific PD, and in a substantial minority (37%) of cases no PD is found. The unspecified category is by far the most frequent PD in patients with ATPD. The sample will be followed up and reassessed.