Objectives To investigate the incidence of cancer in arthritis patients treated with or without TNF alpha inhibitors (TNF-I). Methods Arthritis patients from the DANBIO database were followed-up for cancer in the Danish Cancer Registry during 2000-2008. Results Hazard ratio for cancer overall was 1.02 (95% confidence interval (CI) 0.80-1.30) in 3347 TNF-I-treated RA patients compared to non-treated. Excess among TNF-I-treated was found for colon cancer (HR 3.52 (95% CI 1.11-11.15), whereas 6 and 0 ovarian cancer cases were observed in treated and non-treated patients, respectively. Compared to the general population, TNF-I-treated RA patients had increased risk for cancer overall, cancer in lymphatic-haematopoietic tissue and non-melanoma skin cancer, while non-RA patients had no increase in overall cancer risk. Conclusions Our results suggest that TNF-I therapy in routine care is not associated with an overall excess of cancer in arthritis patients, but observed increased risks of colon and ovarian cancer need further investigation.