Tollund Man is one of the most famous Iron Age bog bodies due to his well-preserved head. Since he was unearthed in 1950 in Bjældskovdal, Denmark, he has been subjected to several scientific investigations, but until now no attempts to reconstruct his general diet through isotope analyses have been conducted. Furthermore, previous radiocarbon (14C) analyses have only been able to date him broadly to the 3rd–4th century BC. In this study, stable isotope measurements (δ13C, δ15N) on bone collagen from Tollund Man’s femur and rib showed that the diet of Tollund Man was terrestrial-based and that the crops he ate probably were grown on manured fields. Accelerator mass spectrometry (AMS) 14C dates were obtained on both the <30kDa and >30kDa fractions of ultrafiltered collagen. Results showed that the ultrafiltration removed contamination from older substances from the burial environment. The femur was dated to 2330±23 BP, the rib to 2322±30 BP. These dates statistically agree with a previously published AMS 14C age on skin. By combining the new dates with the previous date of his skin it was possible to narrow down the age of Tollund Man to the period 405–380 cal BC (95.4% confidence interval).