Background. ICD-10 acute and transient psychotic disorder (ATPD; F23) and DSM-IV brief psychotic disorder (BPD; 298.8) are related diagnostic concepts, but little is known regarding the concordance of the two definitions.

Method. During a 5-year period all in-patients with ATPD were identified; DSM-IV diagnoses were also determined. We systematically evaluated demographic and clinical features and carried out follow-up investigations at an average of 2·2 years after the index episode using standardized instruments.

Results. Forty-two (4·1%) of 1036 patients treated for psychotic disorders or major affective episode fulfilled the ICD-10 criteria of ATPD. Of these, 61·9% also fulfilled the DSM-IV criteria of brief psychotic disorder; 31·0%, of schizophreniform disorder; 2·4%, of delusional disorder; and 4·8%, of psychotic disorder not otherwise specified. BPD showed significant concordance with the polymorphic subtype of ATPD, and DSM-IV schizophreniform disorder showed significant concordance with the schizophreniform subtype of ATPD. BPD patients had a significantly shorter duration of episode and more acute onset compared with those ATPD patients who did not meet the criteria of BPD (non-BPD). However, the BPD group and the non-BPD group of ATPD were remarkably similar in terms of sociodemography (especially female preponderance), course and outcome, which was rather favourable for both groups.

Conclusions. DSM-IV BPD is a psychotic disorder with broad concordance with ATPD as defined by ICD-10. However, the DSM-IV time criteria for BPD may be too narrow. The group of acute psychotic disorders with good prognosis extends beyond the borders of BPD and includes a subgroup of DSM-IV schizophreniform disorder.