The study evaluated sexual dysfunction in the course of psychotropic drug treatment among male outpatients at the Psychiatric Hospital, Yaba. It specifically assessed the prevalence of sexual dysfunctions among the patients compared with controls selected from the staff of the hospital. The study also examined the effect of sexual dysfunctions on medication adherence among the patients. Eight hundred respondents, comprising 400 patients and 400 controls from Psychiatric Hospital, Yaba were recruited for this study using systematic random sampling technique. The patients and controls were recruited from a population of 3766 patients and 1089 hospital workers. The patients were assessed with a socio-demographic questionnaire, the Sexual Side Effect Scale for Medication Compliance, the Massachusetts Sexual Functioning Questionnaire and the Structured Clinical Interview for DSM-IV Disorders (SCID). The controls were screened with a socio-demographic questionnaire, the Massachusetts Sexual Functioning Questionnaire and the 12–item GHQ screening instrument. The results showed that 61.5% of the patients were diagnosed with schizophrenia. Other psychiatric disorders present were bipolar affective disorder (21%), psychotic disorder not-otherwise-specified (8.5%), major depression (6.8%) and schizoaffective disorder (2.3%). The mean age of the patients was 35 ±8.5 years and mean age of the controls was 36 ±8.0 years. The patients were mostly single (68.8%) but the controls were mostly married (61%). Most of the patients (65.3%) were also gainfully employed. Most of the patients (67.7%) and controls (91.2%) were sexually active but the controls (67.5%) were mostly engaging in coitus compared with patients (28.8%). Exclusive masturbation was higher among patients (14.8%) than among controls (5.0%). Most of the patients had a poor attitude towards sexual health as they had not been discussing sexual issues with clinicians. They also lacked adequate knowledge about the sexual side effects of psychotropic medications. Tile dysfunction had the lowest ranking in the control group (5.2%). The prevalence of sexual dysfunction among the patients was 69%, range 26% to 62.8% while the prevalence of sexual dysfunction among the controls was 19.8%, range 5.2% to 11.2%. Sexual interest dysfunction was ranked highest among patients (62.8%) whereas orgasmic dysfunction had the highest ranking among the controls (11.2%). Arousal dysfunction ranked lowest in the patient group (26%), whereas erectile dysfunction had the lowest ranking in the control group (5.2%). The prevalence of medication non-adherence was 9.3%, and patients who experienced sexual dysfunction were more likely to report medication non-adherence (p<0.01). Sexual dysfunction was present in all the diagnostic groupings but sexual interest was mostly prevalent among patients diagnosed with schizophrenia. However, arousal dysfunction, orgasmic dysfunction and erectile dysfunction were all more prevalent among patients diagnosed with major depressive disorder with psychotic features. Sexual dysfunction was more prevalent among older patients, the well educated and the unemployed. Sexual dysfunction was also more prevalent among the single and divorced. The major limitation of the study is that the Massachusetts Sexual Functioning questionnaire has not been validated for use in this environment. Others included none matching of the patients and controls for marital status, the absence of medication naïve psychiatric patients as additional control and the use of hospital staffs as controls. In conclusion, the study confirmed previous reports that sexual dysfunction has a high prevalence in psychiatrically ill patients. The study also revealed that sexual dysfunction in the course of psychotropic medications treatment among psychiatric patients is associated with medication non- adherence. This study draws attention to the urgent need to give the required attention to sexual health and functioning of psychiatric patients. This could be done by ensuring that clinicians routinely enquire about sexual problems and also manage them appropriately. Clinicians also need to educate patients properly about the sexual side effects of psychotropic medications.