Background: Suicide has been recognized as one of the commonest causes of death globally and mental disorders have been found to contribute about 70% to 80% of causes of suicide. A number of factors can predict or increase the risk of suicide among those who have mental illnesses.

Aim: This study aimed to look at the factors influencing suicide behavior among mentally ill patients at the University of Port Harcourt Teaching Hospital.

Materials and Methods: This was a cross-sectional study conducted among attendees of Neuropsychiatric Outpatient Clinic of the University of Port Harcourt Teaching Hospital. A structured questionnaire covering socio-demographic characteristics and other factors were self-administered to 75 patients diagnosed with various psychiatric disorders by consultants Psychiatrists and attending the out-patient clinic via a systematic random sampling. Ethical approval was obtained from the ethical committee of the University of Port Harcourt Teaching Hospital and all other ethical provisions were followed. Descriptive and inferential statistics were used to analyze the data. p value ≤ 0.05 was considered statistically significant.

Results: Majority of the respondents were male (81%), single (76.0%), unemployed (36.0%), low income earners (73.4%) and between the ages of 21 and 30 (44%). Majority had tertiary education (58.7%) followed by respondents with secondary education (33.3%). Those who were dissatisfied with life due to mental illness constituted 34.9% while those who were dissatisfied with living were 22.5%. Nineteen (25.3%) of the respondents has had suicidal thoughts while 7(9.3%) had attempted suicide. Major determinant of the suicide behavior were stigmatization from mental illness, advice childhood experience, job loss, substance abuse, history of assault and poor premorbid personality. There was a statistically significant association between suicidal behavior and stigma as well as childhood or family history (χ2 = 3.828, p = 0.05; χ2 = 6.334, p = 0.042), but association between suicidal behavior and drug use, sexual assaults, job loss and query respectively was not statistically significant (χ2 = 0.456, p = 0.5; χ2 = 3.111, p = 0.078; χ2 = 6.921, p = 0.009; χ2 = 0.009, p = 0.922).

Conclusion: Suicide behavior was common among those with mental illness and unemployment, substance abuse, male gender, higher level of education, stigmatization, poor premorbid history, adverse childhood experience are among the factors that could affect suicide behavior. Association exits between suicide behavior and drug use, stigma, childhood or family history, sexual assaults, job loss, and query etc. It is, therefore, important to provide adequate attention and care to the mentally ill to help reduce the prevalence of suicidal behavior among them.