Irregular or delayed attendance at HIV treatment clinics among HIV-positive individuals can have negative implications for clinical outcomes and may ultimately undermine the effectiveness of national treatment programmes. This study explores factors influencing attendance at HIV clinic appointments among patients in a rural ward in north-west Tanzania. Forty-two in-depth interviews (IDI) and four focus group discussions were conducted with HIV-infected persons who had been referred to a nearby antiretroviral therapy (ART) clinic, and IDI were undertaken with 11 healthcare workers involved in diagnosis, referral and care of HIV-positive patients. The Health Belief Model was applied to explore the role of health-related beliefs and the perceived barriers and benefits associated with regular clinic attendance. Perceived susceptibility to HIV-related illnesses emerged as an important factor influencing clinic attendance, and was often manifest through expressions of acceptance or denial of HIV status and knowledge of HIV disease progression. Denial of HIV status was often associated with using alternative healers, and could occur prior to, during, or after starting ART. Perceptions of illness severity also influenced HIV clinic attendance, and often evolved in relation to changes in physical symptoms. Barriers to clinic attendance frequently included health systems factors, while physical and social benefits encouraged regular clinic attendance. Self-confidence in being able to sustain clinic attendance was often determined by patients' expectations or experiences of family support. These findings suggest that multi-faceted interventions are required to promote regular HIV clinic attendance, including on-going education, counselling and support in both clinic and community settings. These interventions also need to recognise the evolving needs of patients that accompany changes in physical health, and should address local beliefs around HIV aetiology. Decentralisation of HIV services to rural communities should be considered as a priority to redress the balance between perceived barriers to, and benefits of accessing HIV treatment programmes.