Introduction:  It is a proven fact that almost all drugs carry the potential to produce undesirable effects in addition to the desired ones. Aim:  The aim of this study is to determine the prevalence, pattern and socio-demographic determinants of adverse drug reactions among patients on HAART attending clinics in hospitals in Imo State Nigeria. Methodology:  This was a hospital-based cross-sectional study carried out among HIV patients attending clinics in hospitals in Imo State.  The 400 participants were selected using a multistage sampling technique.  Data was collected using an interviewer administered, semi-structured questionnaire and analyzed using EPI Info version 3:2:1. Chi-square and regression analysis was used to test association between variables. P-value was set at ≤ 0.05. Results: The mean age of the participants was 41.7±3.0 years with a male to female ration of 1:2. The adherence level to HIV treatment was 85.0%. The prevalence of ADRs in the last 1 year preceding the study was 13.7% and the common forms of ADR experienced by patients was Hematological symptoms (34%), GIT symptoms (21.8%) and skin manifestation (20.0%). Socio-demographic determinants of the occurrence of ADR among the participants were: age 50 years and above (OR: 9.28), female gender (OR: 2.55) and living in a rural area (OR: 4.47). Conclusion:  Though the prevalence of ADR reported in this study was low, there is need to increase the depth of knowledge among HIV patients in the State, monitor patients closely by care givers and find possible ways to increase adherence to HIV drugs which was not optimal among participants. Keywords: Prevalence, Pattern, Adverse Drug reactions, HAART, HIV, Patients, Imo State.