The phenology of intrapuparial development in Oestrus ovis L. is described, based on 302 specimens collected from the head cavities of goats and reared in the laboratory at a photoperiod of 12:12 (L:D) h and 32 and 16°C. Dissection and histology of puparia at pupariation and at 3, 6, 9, 12, 15, 18, 21, 24, 30, 36, 42, 48, 66, and 72 h after pupariation and every day of the intra-puparial period showed that pupariation was achieved in ≈12 h in heavily pigmented larvae (range, 2–46 h in postfeeding period). Larval-pupal apolysis began immediately after pupariation and was completed by 18–36 h after pupariation (prepupal period). The cryptocephalic pupa was found from this time to the 5th d, when head eversion occurred. Pupal-adult apolysis was initiated before head eversion and completed by day 7. The pharate adult presented progressive coloration in compound eyes (transparent, white, yellow, orange, red, brown, silver) while integumental pigmentation and sclerotization were in progress. Adult emergence occurred at 22 and 23 d in males and females, respectively. Changes in the weekly puparial weight of specimens reared under both field and laboratory conditions was described. It was concluded that although the intra-puparial development of O. ovis displayed some unique characteristics, it was essentially similar to other cyclorraphous flies. The actual pupal period of O. ovis lasted from the 2–7 d postpupariation, whereas approximately two-thirds of the intrapuparial period was used for the maturation of the pharate adult.