Two thousand and two heads obtained from slaughtered sheep at the Fars abattoirs (Shiraz, Southern Iran) between April 2006 and April 2007 were examined for the presence of Oestrus ovis larvae. Of the total heads, 995 (49.7%) were infested with O. ovis larvae. O. ovis larvae were observed in both sexes and all age groups in each season of the year. A total of 6264 larvae were collected. The overall larval intensity for the infested sheep was 6.3, with 3.9 in spring, 5.3 in summer, 5.9 in autumn and 7.8 in winter. Prevalence ranged from 23.3% in spring to 80% in winter. Increased infestation was observed in older animals.