Non-communicable diseases like hypertension are increasingly common among individuals living with HIV in low-resource settings. The prevalence of hypertension among people with HIV in Malawi, e.g. has been estimated to be as high as 46%. However, few qualitative studies have explored the patient experience with comorbid chronic disease. Our study aimed to address this gap by using the health belief model (HBM) to examine how comparative perceptions of illness and treatment among participants with both HIV and hypertension may affect medication adherence behaviours. We conducted semi-structured interviews with 75 adults with HIV and hypertension at an urban clinic in Lilongwe, Malawi. Questions addressed participants’ experiences with antiretroviral and antihypertensive medications, as well as their perspectives on HIV and hypertension as illnesses. Interviews were performed in Chichewa, transcribed, translated into English and analysed using ATLAS.ti. Deductive codes were drawn from the HBM and interview guide, with inductive codes added as they emerged from the data. Self-reported medication adherence was much poorer for hypertension than HIV, but participants saw hypertension as a disease at least as concerning as HIV—primarily due to the perceived severity of hypertension’s consequences and participants’ limited ability to anticipate them compared with HIV. Differences in medication adherence were attributed to the high costs of antihypertensive medications relative to the free availability of antiretroviral therapy, with other factors like lifestyle changes and self-efficacy also influencing adherence practices. These findings demonstrate how participants draw on past experiences with HIV to make sense of hypertension in the present, and suggest that although patients are motivated to control their hypertension, they face individual- and system-level obstacles in adhering to treatment. Thus, health policies and systems seeking to provide integrated care for HIV and hypertension should be attentive to the complex illness experiences of individuals living with these diseases.