In ungulates, a set of deciduous teeth is replaced by a set of permanent teeth during their first 2 years of life. Little is known about factors causing variation in timing of tooth eruption, but overall size, condition or mineral deficiencies may play a role. The pattern of incisor (I) and canine (C) eruption was investigated in 2241 yearlings from five populations of red deer Cervus elaphus in Norway during 1964–2001. Before the sampling period (10 September–15 November), I1 had erupted in most yearlings (97%), while eruption of I3 and C had barely started (erupted in 7% and 5% of individuals, respectively). Exactly 50% of the yearlings had erupted I2. Jawbone length was shown to be a main determining factor for eruption of I2. However, for a given jawbone length, there was large variation among populations in the proportion of yearlings with erupted I2 (from <20% to >75%). Females got their permanent I2 earlier than males. Tooth eruption was found to be later with increasing local deer density, even after correcting for body weight. There was a residual effect of body weight (a measure of condition) after body size (measured as jawbone length) was controlled for in one of five populations, indicating that overall condition may influence timing of tooth eruption in this area. There was no evidence that calcium was limiting for eruption, as no correlation was found between timing of eruption and limestone in bedrock. Since there is large variation in timing of tooth eruption among red deer populations even after controlling for differences in phenotype and environmental factors, genotypic variation may also play an important role for tooth eruption patterns.