Paratuberculosis was diagnosed in a population of approximately 1,000 free-ranging fallow deer ( Dama dama ) sampled from 1997–98 in the Regional Hunting Reserve of El Sueve (Asturias, Spain). Five of eight animals observed with diarrhea were diagnosed as having paratuberculosis on the basis of gross lesions at postmortem examination and histopathology. In two deer, Mycobacterium avium subsp. paratuberculosis was cultured and identified by polymerase chain reaction. Indirect enzyme-linked immunosorbent assay and immunodiffusion tests were used to evaluate sera from 33 adult deer from this population. All fallow deer tested were seronegative.