An epidemiological study on Metagonimus yokogawai infection was performed in Samcheok-gun, Kangwon province during the period from November 1983 to October 1984. Formalin-ether concentration technique and Stoll's dilution egg counting method were employed to figure out the prevalence and infection intensity of M. yokogawai infection. The results are summarized as follows: The prevalence of M. yokogawai infection was 13.3 % among 1,172 examined; 18.0 % (114 out of 632) in male and 7.8 % (42 out of 540) in female. The prevalence rates were different by stream; 15.5 % in Ohsip-chon (stream), 11.8 % in Maeup-chon and 1.6 percent in Gagok-chon. Along the basin of Oship-chon; 8.2 % at the lower reaches in Samcheok-eup, 25.9 % at the middle reaches in Miro-myon and 6.2 % at the upper reaches in Dogeoe-eup, respectively. By age group, the highest rate (18.3~20.2 %) was observed in 30~49 years of age (male : 24.1~28.7 %, female 11.2~13.2 %). By social strata, the positive rate was 15.0 % (120 out of 799) in general inhabitants and 9.7 % (36 out of 373) in school children. Intensity by EPG count in feces was 419 in average; the light infection (less than 400 EPG) was 70.4 %, moderate infection (401~1,000 EPG) 19.4 % and heavy infection (more than 1,001 EPG) 10.2 percent respectively. All the 67 sweetfish (length 10.3~18.5 cm) which were caught from Ohsip-stream were infected with metacercariae of M. yokogawai and the number of metacercariae detected were 382 per fish in average (323 in June and 382 in September). Experiences of intake of raw fresh-water fish [Plecoglossus altivelis and Leuciscus (Tribolodon) sp.] were present in 50.3 % (354 out of 704) of the inhabitants along Ohsip-stream according to questionnaire study. The results of this survey indicated that the middle reaches of Ohsip-stream in Miro-myon, Samcheok-gun is the endemic region for M. yokogawai infection.