This study was carried out to estimate the prevalence, larval burden and some risk factors of ovine oestrosis in 328 heads of randomly selected sheep slaughtered in one year at Van, eastern Turkey. Of the total heads, 127 (38.71 %) were infested with Oestrus ovis (Linnaeus, 1761, Diptera: Oestridae) larvae. The prevalence of O. ovis was 51.68 % in summer, 40.69 % in spring, 35.80 % in autumn, and 23.61 % in winter. The differences between seasons were statistically significant (P<0.05). Out of a total of 511 larvae collected, 17 % were L1, 29 % L2, and 54 % L3 larvae. All three larval instars were observed in all study months, apart from the fact that no first-stage larvae were seen in December and March. The overall larval intensity for the infested sheep was 4.02, with 3.42 in spring, 3.80 in summer, 4.03 in autumn and 5.82 in winter. The infestation rates were 41.26 % in female and 34.42 % in male sheep. The infestation rate in sheep less than 2-years-old was 23.33 %, in those 2 to 4 years-old 36.42 % and inj those older than 4 years old 48.43 %. Sheep with dark head color had a higher risk than sheep with white and spotted heads (P<0.05).