Objective: Several surveys have demonstrated increased psychiatric admissions during the paramenstrual phases of the menstrual cycle. Some data suggest an exacerbation of symptoms during the premenstrual and menstrual phases. This study is aimed to clarify the relationship of the menstrual cycle to acute psychiatric illness. Method: In 210 consecutive female admissions to the psychiatric inpatient service of Bakirkoy State Mental Hospital, menstrual cycle phase at the time of emergency admission were assesssed. Patients who were pregnant, menopausal, posthysterectomy, taking birth control pills, or whose menstrual cycle lengths were less than 24 days or more than 35 days were excluded from the study. The subject group contained a wide range of psychiatric diagnoses. Results: Consistent with other studies, a significantly greater number of admissions were found to be during the "menstrual" and "premenstrual" phases than at other times;59.1% of psychiatric admissions occured during the paramenstrual phase (33.3% premenstrual, 25.8% menstrual). There were no significant phase differences found between affective (unipolar depression, bipolar depression, mania and mixed episode) and schizophrenic (schizophrenia, schizophreniform disorder, delusional disorder, brief psychotic disorder, schizoaffective disorder, psychotic disorder NOS)spectrum patients. Conclusion: In this study, exacerbations in psychotic disorders were found to be correlated with the premenstrual and menstrual phases of the cycle. Despite the methodological limitations (accurate determination of menstrual cycle phases, the heterogenity of the patient group, use of medication etc.), this finding of paramenstrual increase in rate of emergency psychiatric admissions may have important clinical, etiological and therapeutic implications.