“…Psychiatry, 1990 ,29,3:407-412 . Key Wo rd s : ge netic , familia l, obsessi ve compul sive disorde r (OCD) .Since the classic report of Au brey Lew is in 1936 , seve ra l cli nica l investiga tors have reported increas ed prevalence of obsess ive co mpulsive disorder (OC D) among first-d egree relatives of obsessive co mpulsive (OC) pati ent s , (0 % to 40 %) (Lewis , 1936;Brown , 1942; Rud in , 1953; Rasmussen and Ts uang , 1986) , although others have found no increases (Ros enberg, 1967; Coppen et aI., 1965; McK eon and Murray , 1987). Rates higher than expected in relatives sugges t a ge netic co ntribution to etio logy and furth er suppor t is provided by repor ts of grea ter co ncorda nce for OCD among monozygot ic twin s than dizygot ic twins (Ino uye, 1965; McKeon ct al.…”