The study was conducted on the mouflon-derived horned sheep of the preserved Polish Heath Sheep breed. In this study, basic skull measurements of 24 skulls of the rams of different age: 1 day, 90 days, 210 days, 270 days, 3 and 6 years, were analyzed. The weight of each skull was determined, as well as 43 craniometric characteristics were measured, and cranial cavity volume and viscerocranial and neurocranial indices were calculated. From birth to the age of 6 years, the greatest length of the skull, the condylobasal length and the length of the cheek-tooth row increased two-fold. To day 210 of age, the bony housing for eyeball and its organs grew intensively. To day 270 of age, the largest increase was characteristic of the elements of the angular length of the neurocranium and its breadth. The structural elements characterizing both the breadth and the length of the viscerocranium developed to the age of 6 years. A significant (P0.05), decreasing with age, value of the cephalic index was observed, being mostly affected by development of the squamous part of the frontal bone with its orbital part and the orbital margin.