Pathologic consequence of tattooing is relatively rare, but in light of the great number of persons in military service, where tattooing seems to be popular, consideration of the complications seems worth while.Four unusual cases of patients with cutaneous lesions in tattoos are reported. One patient had Boeck's sarcoid, in which the cutaneous eruption was limited solely to the tattooed areas on the body and involved all the various colors of the tattoo. The cutaneous eruption was only a single manifestation of generalized sarcoidosis. Another patient had secondary syphilis with the cutaneous lesions involving multi-colored tattoos, including the red areas. These tattoos were applied in Hawaii, and presumably the red dye was not the usual cinnabar (mercuric sulfide). As a general rule, the cutaneous lesions of secondary syphilis do not involve the red areas because of the treponomicidal action of mercuric sulfide.In the third case the characteristic eruption of discoid lupus erythematosus was present. It began over the red areas of a tattoo on the patient's forearm. It has been stated that mercuric sulfide is a photo-sensitizing agent, and it is believed that this explains the localization of the eruption in this case. The fourth patient had eruption, caused by mercury sensitivity, in an area of tattoo. The eruption was noted soon after the tattooing was done, and it persisted for seven years.