This study was conducted to investigate allometry of head growth patterns in the grass snake (Natrix natrix (Linnaeus, 1758)). Although male and female grass snakes differ in relative head size, their head growth patterns follow similar trajectories. The sexual differences are roughly constant during ontogeny. Most head dimensions grow with negative allometry or isometry with respect to the snout–vent length except head width, which grows with positive allometry in both sexes.