This study examines the stability of ICD-10 diagnoses of patients admitted to Al Ain (United Arab Emirates) inpatients psychiatric unit during the period from November 1993 to August 1995. Diagnostic stability is a measure of the degree to which diagnoses remained unchanged at a later hospital admission. One hundred and seven patients were admitted more than once during this period, accounting for 168 readmissions. High levels of diagnostic stability were found for ICD-10 Fl-psychiatric disorders (100%), F2-schizophrenia (87%), F3-bipolar disorders (87%) and F3-depressive disorders (73%). A poor level of stability was found for patients with neurotic, stress related and adjustment disorders (F4), ranging from zero for somatoform disorders to 50% for generalized anxiety and panic disorders. Poor levels of stability were also found for other psychoses (excluding schizophrenia and affective psychoses) and personality disorders. We conclude that the introduction of ICD-10 as a formal diagnostic system has greatly improved the temporal stability of the most commonly encountered psychiatric disorders (ICD-10 Fl to F3 disorders), confirming the construct validity of those psychiatric disorders. Further investigations are required to evaluate the diagnostic stability of neurotic and other psychotic disorders.