Teeth are vital for mammal performance and especially in ungulates relying on mechanical decomposition of plant material for effective microbial digestion and energy uptake. The main focus of the role of teeth in ungulate life histories has been on tooth wear, while no one has addressed to what extent deviation from the natural set of teeth (maldentition) causes variation in individual fitness components. Based on mandibles from 41,066 individual red deer (Cervus elaphus L.) collected from 1969 to 2001, we tested whether maldentition had an effect on individual body condition and whether this effect depended on environmental harshness. Females with maldentition (0.6% of the population) were in a poorer condition than individuals without tooth anomalies and the effect increased during unfavorable climatic conditions. The effect of maldentition in males was less clear. This study indicates that a well-functioning set of teeth is essential for mammal performance, and that selection pressure against (dental) anomalies is more pronounced when climate is unfavorable.