The incidence of basal cell carcinoma and squamous cell carcinoma (non-melanoma skin cancer) is increasing in the U.K., and the importance of this has been recognized in the 'Health of the Nation' target of halting the annual increase in the incidence of skin cancer by the year 2005. An accurate assessment of incidence is necessary both in meeting this target and in planning skin cancer services. We have examined the ways in which basal cell carcinoma and squamous cell carcinoma are diagnosed and treated in Greater Glasgow and have determined how many of these tumours are, recorded by the West of Scotland Cancer Registry. Our results show that there is under-registration of both basal cell carcinoma and squamous cell carcinoma. Overall, 39 of 127 basal cell carcinomas (31%; 95% confidence interval [CI] 23-39%) and 11 of 25 squamous cell carcinomas (44%; CI 26-63%) were not registered by the cancer registry. We also showed that dermatologists rarely treat clinically suspicious tumours without obtaining pathological proof of the diagnosis. Accurate data collection by selected representative cancer registries is suggested as a possible solution.