Safe care in general practice for people living with HIV requires early diagnosis of undetected infection and safe co-prescribing with antiretroviral therapy (ART). To evaluate safe co-prescribing in general practice patients who are taking ART, and to describe missed diagnostic opportunities for undiagnosed HIV infection in primary care. Retrospective case-notes review in general practices within NHS City and Hackney Primary Care Trust (PCT), London, UK. All general practices in NHS City and Hackney PCT were invited to participate. Patients known to be HIV positive were identified using Read Codes. Each practice undertook retrospective case-notes reviews on specialist correspondence, coding of ART, prescribing of common contraindicated drug pairings, and missed opportunities for HIV diagnosis. In total, 31/44 (70.5%) practices participated, and 1022 people living with HIV were identified. Practices had received HIV clinic letters for 698 of those 1022 (68.3%) patients in the previous 12 months. Of the 787 patients known to be prescribed ART, only 413 (52.5%) had correct drug codes recorded; 32/787 (4.1%) were receiving specified contraindicated drug pairings. In total, 89 patients were eligible for their case-notes to undergo a retrospective review of occurrences that took place pre-diagnosis. In the 2 years preceding diagnosis, these 89 had attended 716 face-to-face GP consultations, of which 123 (17.2%) were for indicator conditions. Fifty-one of these patients (57.3%) presented at least once with an indicator condition (interquartile range 1-3; median 2). In a large-scale evaluation of GP records of people living with HIV, gaps in ART recording and co-prescribing were identified, and evidence demonstrated missed opportunities for diagnosis within general practice. Specialists and generalists must communicate better to enhance safe prescribing and reduce delayed diagnosis.