A prospective controlled study was made on the effect of adenoidectomy performed on 105 children. For various reasons, mainly severe long-standing nasal obstruction, 29 children were omitted from the study. The remaining 76 children were randomly divided into two groups, one adenoidectomy, and one control. Both groups were slightly reduced in number due to drop out. Thus 36 adenoidectomized children were followed during one year and 35 children during two years. The corresponding numbers for the children in the control group were 37 and 33. The incidence of common cold, purulent and serous otitis media and moderate nasal obstruction was compared in the two groups. A considerable reduction in the incidence of these variables was observed in both groups. The occurrence of moderate nasal obstruction was reduced more among the operated than among the unoperated children. The difference was only slightly significant during the first and not at all during the second year. Regarding the other variables, the differences were not significant, implying that adenoidectomy seems to have no effect on the incidence of common cold, serous and purulent otitis media.