It has been debated whether the reported increased risk of Hodgkin's lymphoma (HL) after tonsillectomy could be due to some underlying factor rather than the surgery itself. We studied whether not only tonsillectomy but also tonsillitis was associated with HL. This nationwide cohort study included all Danish residents during 1977-2001. Information on a diagnosis of tonsillitis, tonsillectomy, or HL was obtained from national registries. During 124 million person-years we observed 2,988 HL patients of whom 58 were tonsillectomized (most with preceding tonsillitis) and 14 were diagnosed with only tonsillitis at more than 1 year before HL diagnosis. Tonsillectomy was associated with a significantly increased HL risk in persons under 15 years of age as follows: 1-4 years after tonsillectomy, relative risk (RR) = 3.9 [95% CI: 1.4-11; n = 4]; >5 years after tonsillectomy, RR = 3.5 [1.4-8.5; n = 5]. No young cases of HL occurred among persons diagnosed with only tonsillitis. In contrast, 1-4 years after a hospital diagnosis of tonsillitis without subsequent tonsillectomy we found an increased HL risk in persons aged 15 years or above as follows: 15-34 years of age at HL diagnosis, RR = 3.5 [1.6-7.7; n = 6]; 35+ years, RR = 5.9 [2.2-16; n = 4]. Age at tonsillitis or tonsillectomy did not modify HL risk within the 3 age strata. An increased HL risk was found both after tonsillectomy and after an isolated diagnosis of tonsillitis. These results suggest that tonsillitis is a risk factor for HL and not that, as previously reported, only the surgical removal of tonsils is a risk factor.