A method is described to determine the age of red cod using the bands in sectioned otoliths. The technique was validated by examining the state of otolith margins over a 1‐year period, and by following the progression of length modes in length‐frequency distributions (for age classes 0+ to 3+). Von Bertalanffy growth parameters are estimated for red cod off the south‐east coast of the South Island. Few fish appear to live longer than 4 years. Because of the few age classes in the population at any time, age distributions may be obtained for most of a sample using length modes.