To provide an age-length key for use in modelling the age structure of the Patagonian toothfish stock around the Falkland Islands, we used otoliths to estimate the age of a sample of 1893 Patagonian toothfish (Dissostichus eleginoides) captured by trawl and in the longline fishery. We used a thin section grinding machine to reveal a transverse plane through the otolith nucleus and between crenellations. Two readers undertook one reading each of the sections, estimating age using criteria agreed at the CCAMLR Otolith Network. Age estimates by the experienced reader were unbiased relative to reference ages. However, the second trainee reader consistently over-estimated the age of younger fish, and her readings were not used in the analysis. Estimates of the Von Bertalanffy parameters were L8 = 129.3, K = 0.12 and t0 = -1.55 for females; for males, L8 = 110.9, K = 0.156 and t0 = -1.12. Using these age data, we estimated total mortality to be Z = 0.27.