In a Danish nationwide prospective study of in situ carcinomas and atypical lesions of the breast, 88 women, comprising 69 patients with lobular carcinoma in situ (LCIS) and 19 patients with combined lobular and ductal carcinoma in situ (LCIS + DCIS), were accrued from 1982 through 1987. All cases were treated with excision only. Within a median follow-up time of 61 months, a recurrence rate of 17% (15 cases) was found, excluding nine cases of refinding of LCIS. No contralateral recurrences occurred. The recurrences were in eight cases invasive carcinomas (IC), in six cases LCIS + DCIS, and in one case DCIS alone. The recurrence rates among cases of LCIS and of LCIS + DCIS were not significantly different. The histopathological review included an estimate of the number of lobules with LCIS and nuclear size, both of which were significantly related to recurrence. The risk of developing IC was calculated to be increased by a factor 11 as compared with the reference population.