Antiretroviral therapy places extraordinarily high demands on adherence, since non-adherence affects both individuals and society due to the spread of resistant viral strains. The aims of the thesis were to investigate the prevalence of adherence in Swedish HIV-infected patients, changes in adherence over time, and factors associated with adherence, including patients’ readiness to adhere. Further, to investigate the collaboration between nurses, doctors and pharmacists after the introduction of a HIV-clinic satellite pharmacy. Data were collected via two cross-sectional patient surveys in 1998 and 2002, qualitative interviews with health care personnel at a major HIV clinic, and a nation-wide, cross-sectional patient survey in 2003-2004. The level of adherence improved from 28% in 1998 to 57% in 2002, possibly due to simplified treatment and a new multi-professional treatment model at the clinic. The proportion of adherent patients was 63% in the nationwide survey. Factors associated with adherence were high age, high quality patient-provider relationships, no drug or alcohol problems and shorter time on treatment. A hypothesized structural equational model, using readiness and adherence as separate latent concepts, was tested and found to support readiness as a distinct factor influencing adherence. The health care personnel believed that conventional pharmacies had several disadvantages in serving the HIV infected population. They found the HIV-clinic satellite pharmacy valuable, since it contributed to increased communication and trust between the health care professions, and improved teamwork in medication management.In conclusion, the level of adherence increased over time, and several factors associated with adherence were identified. Improved collaboration between health care professionals may enhance treatment support, and increased attention should be given to interventions that focus on the individual’s readiness for behavioural change in order to optimize treatment outcomes.