Women with carcinoma in situ (CIS) of the cervix uteri, notified to the population-based Cancer Registry of the Swiss Canton of Vaud between 1974 and 1993, were actively followed up to 31 December 1993 for the occurrence of subsequent invasive neoplasms. Among 2190 incident cases of CIS, followed for a total of 22,225 person-years, 95 metachronous cancers were observed vs 77.9 expected, corresponding to a significant standardised incidence ratio (SIR) of 1.2. Ten cases of invasive cervical cancer were observed vs 3.0 expected (SIR = 3.4, P < 0.01), the excess being larger in the first 10 years since CIS diagnosis. A total of 11 cases of four major tobacco-related sites (lung, mouth or pharynx, oesophagus and urinary bladder) were observed vs 5.1 expected, corresponding to a significant SIR of 2.2. The excess was observed > or = 10 years after CIS diagnosis. There was also an excess of non-melanomatous skin cancers (29 observed, 16.9 expected, SIR = 1.7; P < 0.01), but not of skin melanoma and of any of the other neoplasms considered, including breast and corpus uteri. This population-based study, therefore, finds an excess of invasive cervical cancer in the short term after CIS diagnosis, and a medium- to long-term excess risk of tobacco-related and non-melanomatous skin neoplasms. These findings are discussed in terms of increased surveillance and case ascertainment after CIS, and of potential shared risk factors (tobacco and/or viral infections).