A study sample of 88 patients suffering from delusional beliefs was examined from first admission to follow-up. From the time of index admission, global functioning differs when distributed in accordance with ICD-10 categories. Patients with the discharge diagnoses affective disorder and acute and transient psychotic disorder have similar and optimistic perspective. The most pessimistic perspectives apply to patients with schizophrenia and an intermedium, but a rather pessimistic position also applies to patients with persistent delusional disorder. According to the discharge diagnosis following first admission, the score of global assessment functioning (GAF) at follow-up (8 years) is: schizophrenia 37; affective disorder 73; persistent delusional disorder 47; and acute and transient psychotic disorder 70. Generally, short-term outcome bears close resemblance to that of middle-term observation. During the observation period, 13 patients died. Amongst the surviving 75 patients, diagnosis at follow-up differed from that given at first-admission discharge, in eight cases using ICD-10 and in ten cases using DSM-III-R. Therefore, the use of ICD-10 as well as DSM-III-R enables clinicians to estimate a high stability (89%) diagnostic category with minimal delay.