Records of 120 patients with two and 16 with three primary cancers were evaluated. There were 49 males and 71 females among the double primaries with ages ranging from 27-102 years (average 68 years at the time of fist cancer). Of 35 breast cancer patients 16 new primaries developed in the opposite breast and other sites including four colon, three lung, and three endometrium. Of 20 colon cancer patients second primaries occurred in 1 1 sites most commonly colon (four) and lung (three). The frequency of second primaries may be skewed by the fact that patients with lethal cancers did not live long enough to develop them. This is borne out by the fact that 74 of the 120 patients were alive at the time of the study, implying a highly favorable group of patients. The interval between primaries was longer in females than males ( P < 0.05) and this difference disappeared when breast and endometrial cancer were eliminated. When age was evaluate as a factor younger patients appeared to have a longer interval between primaries ( P = 0.24) and this became significant for breast patients under age 55 years (91 months vs. 36 months) ( P < 0.05). The stage of the second breast primary bore no relationship to the interval between primaries.