Although Mycobacterium bovis infection is commonly reported in red deer (Cervus elaphus), potential differences in the effects of infection on male and female animals in terms of body condition and clinical biochemistry have not been reported. Between November 2000 and January 2006, serum and biometrical data were collected post-mortem from 88 red deer. M. bovis-infected deer, particularly males, were typically older, heavier and in poorer body condition than uninfected animals. Serum triglyceride, cholesterol (both particularly in males) and total protein concentrations were lower, whereas serum creatinine (more evident in females), and immunoglobulin G and M concentrations were higher in the infected deer. These sex-related differences in the response to M. bovis infection in red deer should be considered when undertaking epidemiological assessments and designing disease control strategies as they may reflect differing roles of male and female animals as potential reservoirs or disseminators of disease.