HIV infection continues to be a major health concern although current drug treatments, which are based on combinations of drugs, are generally very effective and an increasing proportion or HIV-infected individuals are living to older age. However, some individuals have a poor response to treatment, largely due to an inability to tolerate their drugs, poor adherence to therapy or the development of HIV strains that are resistant to the drugs used.

As the HIV epidemic has increased in size, and mortality rates have dropped, the HIV-infected population in the UK has become more diverse. The UK CHIC Study makes it possible to conduct research using information collected on different groups of people infected with HIV in the UK. For example, older people now make up an increasing proportion of those with HIV, and they can have different health-care requirements. Also, the way that an individual's immune system responds to treatment for HIV varies with age, and the UK CHIC study data will enable investigation of the possible adverse effects of long-term drug treatment in an older population that may have other non-HIV related health problems.

HIV infection may contribute to an increased risk of several serious events that had previously been thought to be unrelated to HIV, including certain cancers, cardiovascular disease and liver failure. Research suggests that earlier treatment for HIV may have a greater benefit, so it is now recommended that people with HIV start antiretroviral treatment. The drugs used and the way that these drugs are combined have changed over time, so one of the key aims of the UK CHIC study is to use the data to monitor the way people's health responds to drug treatment, both in those that are new to taking anti-HIV drugs and in those who are already on treatment.