In our study, for the first time, it was possible to investigate other cancer risks in a relatively large group of patients with HS over 3 decades. Increases were found for several cancer types, most importantly buccal cancer and primary liver cancer. We have no information of the alcohol-drinking habits of our cohort, and, to our knowledge, no such studies exist, but the increased incidence of primary liver and buccal cancer might be an indication of excessive drinking among patients with HS. Although the excesses remained practically unaltered in the stratum of patients with no recorded alcoholism, the possibility of residual confounding of alcohol abuse cannot be excluded, since probably only a small proportion of alcohol abusers will be given a co-diagnosis of alcoholism when they are hospitalized for other reasons. According to epidemiological data, cigarette smoking seems to be involved in many skin diseases as reviewed previously.23 We have no information on the smoking habits of our patients, but in a questionnaire study of 63 patients with HS, 89% were smokers compared with 46% in a matched-pair control group.24 Similar results regarding smoking habits and HS were found in a recent retrospective study.25 Therefore, substantial confounding by smoking cannot be ruled out, since the risk of lung cancer (SIR, 1.7; 95% CI, 0.6-4.1) and mortality from lung cancer (standardized mortality ratio, 1.7; 95% CI, 0.5-3.9) were increased. The reason for this relationship between the presence of HS, buccal cancer, liver cancer, and cancer in general, if true, and causal, is unclear. However, microbial or lifestyle factors or genetic predisposition are suggested to be included in the considerations. The major strength of our study is the internal validity, that is, the stringent cohort design with no losses to follow-up and virtually complete cancer ascertainment. The epidemiological approach ensured that our patients were representative of hospitalized Swedish patients with HS, thus benefiting the external validity. Moreover, the restriction to patients admitted to hospitals probably minimizes misclassification of the studied condition. However, several limitations should also be noted in the interpretation of our findings. First, owing to the rarity of HS, the small numbers of expected cases of some cancers in this cohort make the risk estimates highly sensitive to chance effects. Second, because we used hospital discharge data to identify our cohort, we may have selected patients with the most severe form of HS26 and, thus, artificially increased the likelihood of finding other serious diseases. Moreover, hospitalized patients may have an excess of comorbidities, in turn, associated with cancer risk. The closer surveillance of hospitalized patients may also introduce some ascertainment or detection bias for skin, breast, and prostate neoplasms. However, the excess risk for all-site cancer, buccal cancer, liver cancer, and nonmelanoma skin cancer persisted after 10 years of observation, which argues for a true relation with HS. Third, information on potential confounding factors, such as cigarette smoking, alcohol drinking, and occupational exposures was unavailable for adjustment. Finally, we could not separate HS from some other skin diseases (ie, pompholyx, bromhidrosis, and chromhidrosis) during the 1987-1996 period. Thus, our cohort may contain some patients who did not have HS. However, no material difference of cancer risk pattern between the 2 periods (1965-1986 vs 1987-1997) was observed, which suggests no important influence on our results by this misclassification of exposure.