The objective of the study was to test the research hypothesis that the surface area of the medullary bone is correlated with other indicators of body condition. The study also focused on identification of potential differences in and with carcass weight fat parameters and carcass weight between forest and field ecotypes of roe deer. The area of the medullary cavity was measured using DIRA 200 software. Metacarpal bone III+IV, proximal phalanges III and IV, and middle phalanges III and IV were measured as well. The study included 38 female European roe deer (Capreolus capreolus) aged 3-5 years. The results revealed a statistically significant negative correlation between the surface area of the medullary cavity in metacarpal bone III+IV and the kidney fat index KFI (rs = −0,483; P < 0,05) and the weight of the perirenal adipose tissue (rs = −0,362; P < 0,05). No correlation was shown between the area of the medullary cavity of metacarpal bone III+IV and the doe carcass weight (rs = 0,093; ns). The size of the medullary cavity is an anatomical parameter that is not susceptible to cyclical changes in environmental conditions. The study showed that it is independent of body weight and determines the amount of bone marrow and hence the amount of accumulated fat reserves. We believe that, alongside biometric measurements, the surface area of the medullary cavity can be a good parameter for assessment of the individual quality of roe deer and for comparison of populations.