Paratuberculosis was diagnosed in one 18-month-old and two 30-month-old hinds in a herd of 70 red deer (Cervus elaphus) in Ireland. Loss of condition and intermittent diarrhoea were the main clinical findings. Clumps of acid-fast organisms were found in the faeces of the three deer. Post mortem examination of one deer showed a slight swelling and pallor of the intestinal tract and associated lymph nodes. Histopathology showed a severe, granulomatous enteritis and lymphadenitis, with extensive cellular infiltration, notably with epithelioid macrophages containing numerous acid-fast organisms. Mycobacterium paratuberculosis was isolated from intestinal and lymph node samples. Paratuberculosis was also confirmed in one of nine clinically normal, yearling stags, sampled at slaughter. Complement fixation tests and enzyme-linked immunosorbent assays gave higher readings for clinically affected deer than healthy ones. Acid soil on the farm was believed to be a contributory cause.