The COVID-19 pandemic has led to patients delaying or forgoing necessary health care, which can contribute to diagnostic and treatment delays.  This retrospective cohort study used primary care data to investigate the indirect effect of the COVID-19 pandemic on primary care health care use and subsequent diagnoses among residents in a poor, urban area in the United Kingdom. Between March and May 2020, there was a 50% reduction in expected diagnoses for mental health conditions, as well as substantial decreases in diagnoses and associated medication prescriptions for circulatory system diseases and type 2 diabetes.