The results are given of a questionnaire study to determine the range of difficulties that doctors notice in their work due to congenital colour vision deficiency (CCVD). The study is primarily qualitative. A questionnaire was sent to 40 self-selected doctors, 35 of whom were general practitioners (GPs). All were administered a number of colour vision tests to assess the type and severity of their deficiency. Many difficulties and some ways of overcoming them were reported. Those with a mild deficiency reported fewer difficulties and this relationship was significant. Twenty-three of the doctors also reported difficulties as medical students and their answers are given verbatim. The results are discussed in relation to other studies and data on colour vision. The reasons for and against screening medical students for this deficiency are considered and it is concluded that there is a strong case for screening.