AbstractForty Red (Sciurus vulgaris) and thirty‐five Grey squirrels (S.carolinensis) have been subjected to full post‐mortem examinations since 1967. The results, together with other reports of disease in Britain affecting free‐living squirrels, are discussed. There appears to be a higher incidence of disease in Reds than in Greys.Parapoxvirus infection, which closely resembles contagious pustular dermatitis or orf of sheep, appears to be common in Reds in Norfolk, but does not appear to occur in Grey squirrels. Coccidiosis (Eimeria sciuroruminfection) is common in Reds. Both species of squirrels frequently harbourEimeriaspp. parasites in the intestinal tract. Other protozoa that occur include haemogregarines (probablyHepatozoonsp.) andToxoplasma.Helminths are relatively uncommon, butEnterobiusspp. were found in the gut of Reds. Both species of squirrels are commonly infested with fleas, mainlyMonopsyllus sciurorumin Reds andOrchopeas howardiin Greys. Lice, especiallyNeohaematopinus sciuri, and ticks (Ixodes ricinus) also occur in both species.In spite of reports to the contrary, there is no proof that either species of squirrels contract mange caused bySarcoptesmites. It is likely that alopecia due to ectoparasitism in both species and parapoxvirus infection in Reds have been mistaken for mange. Fungal and bacterial infections appear to be unusual, althoughPasteurella multocidainfection was diagnosed in a Red andYersinia enterocoliticain a Grey squ