Health impact assessment (HIA) is internationally identified as a mechanism for ensuring that potential health impacts of project proposals are considered before project implementation. This study examined the inclusion of HIAs in environmental impact statement (EIS) and their translation into planning obligations of a dam project in Lesotho. A framework premised on the general systems theory, and integrating EIS contents, environmental management plans and monitoring obligations in post dam construction was used as the analytic lens. A review of the EIS was conducted to assess HIAs covered during the environmental impact assessment (EIA) of the dam. Data drawn from selected household questionnaire interviews and analysis of related documents was used to assess the extent of HIA mainstreaming into planning and monitoring obligations in post dam construction. Results showed inclusion of HIAs in EIS, including endemic diseases such as sexually transmitted infections (STIs) and HIV/AIDS, acute respiratory infections, pharyngitis, hypertension, influenza and diarrhea. Social, economic and environmental conditions were identified as major determinants of health; while mental and nutritional determinants of health were less discussed. The results also showed that some HIAs included in EIS influenced decision-making in relation to raising awareness of health issues in the community. Deficiencies were however reported by respondents in relation to mainstreaming of several HIA recommendations. HIAs can be useful in promoting community health and mitigating adverse impacts of decisions made by project proponents.