Introduction: Sleep disturbances amongst those with psychiatric disorders are quite common and may occur as a primary disorder or in association with psychiatric or organic disorders. Aim: To study the pattern and prevalence of sleep disturbance among psychiatric outpatients and to study sociodemographic characteristics associated with hypersomnia and narcolepsy in this population. Methods: It was a cross sectional descriptive study of consecutively, serially recruited, consenting patients attending the psychiatry outpatient clinic attending a teaching hospital in Lagos, Nigeria, over a ten week period. Ethical approval and informed consent were obtained. The information required was gathered by using the sleep 50 questionnaire and designed socio-demographic questionnaire. Results: Schizophrenia was the most common diagnosis among the subjects (35.9%) followed by major depression (24.5%). Thirty-seven percent of the subjects had at least one sleep disorder; with some having more than one sleep disorder concurrently. The subjects with sleep disorders were mostly young adults (60.3%), single (52.9%), unemployed (60.3%), and female (52.9%). Noise at night was more associated with those who had sleep disorders. Sixteen patients (8.7%) had hypersomnia sleep disorder, while 6.0% had narcolepsy disorder. Of those with narcolepsy, major depression was most prevalent (27.3%), while for hypersomnia schizophrenia was most prevalent (50.0%). Conclusions: The study provides useful data on narcolepsy and hypersomnia among psychiatric patients, with the finding that prevalence rates for both justify the need to improve diagnosis to avoid missed cases.