Understanding the relation between genetic variability, individual fitness and the viability of populations is crucial to ensure their adequate conservation. The most frequently used approach when tackling this question in natural populations is to analyze the correlation between heterozygosity, measured using molecular markers, and traits related to fitness, such as growth, survival, fecundity and developmental stability. Roe deer (Capreolus capreolus) is a species of great importance in Spain that has undergone recent geographical expansion. Understanding all the variables that affect its population dynamics is fundamental to regulate its management and improve its conservation. We examined the relationship between physical condition and individual genetic variability using 30 males captured between May and June (2002) in the Sierra de la Demanda (Burgos). We analysed 11 microsatellites, and individual genetic variability was calculated using standardised individual heterozygosity and mean d2. Relative body weight (residuals of body weight versus body size) is positively correlated with mean d2. High values of this variable are considered to represent high genetic variability since there are greater differences between the alleles inherited from the father and the mother. Thus, our results indicate that individuals with higher genetic variability accumulate more weight for a given size. Previous studies indicate that males in better physical condition are able to defend a larger territory and therefore have access to a greater number of females.