Cancer epidemiology involves using large population studies to describe disease patterns and investigate factors associated with cancer incidence and survival. As the classification of cancers grows ever more complex, with subtypes defined by both conventional histopathological features and novel molecular techniques, it is becoming increasingly important to take account of histopathology in cancer epidemiology research. This review discusses selected examples of where appropriate integration of histopathology into clinical trials and observational epidemiological studies has enabled clinically-important insights into cancer aetiology and survival, including: identifying drugs which are effective in specific molecularly-defined cancer subtypes; demonstrating the value of histopathological variables in predicting survival in breast and ovarian cancers; gaining novel insights into contrasting risk factors for histological types of oesophageal cancer; and using epidemiology to complement histopathology in strengthening the evidence base for the origins and prevention of ovarian cancer. Work is ongoing to integrate histopathology data, including digital slides, into large population health resources such as the 100,000 Genomes Project and the UK Biobank cohort, which will eventually provide rich and complex datasets for exploring histopathology-related questions on a population level. However, expert clinical pathology involvement will be essential to ensure this future work remains scientifically robust and clinically relevant.