Abstract The nutritional adequacy of diets provided by a prison was assessed by analysis of the kitchen menu for 1 week of a 4-week cycle. Dietary intakes were determined using a predefined 7-day diet diary in which prisoners indicated what they had eaten, and how much. A total of 159 prisoners took part in the study. The food provided by the prison kitchen was broadly in line with current dietary recommendations. Vitamin content exceeded recommendations, with the exception of niacin in the vegetarian menu (12.6 mg compared with the reference nutrient intake of 16.8 mg). Selenium content was low in all menus, but particularly in the vegetarian menu in 1997 where it equalled the lower reference nutrient intake (LRNI) (39.5 μg). Food choices made by prisoners resulted in a wide variation in dietary intakes. Fat intake (as a proportion of energy) exceeded the recommended 35% in 82% of diets in 1996, and 64% of diets in 1997. In 1996, 34% of prisoners had intakes above 40% energy as fat. High fat intakes were largely the result of consuming items from the prison shop. Vitamin D intakes were low (3.4 and 3.3 μg in 1996 and 1997, respectively) compared with the recommendation (10 μg) for those with limited exposure to sunlight. Intakes of a number of minerals fell below recommendations, with some prisoners barely meeting the LRNI. This was particularly notable for selenium where 35% of prisoners in 1996, and 60% of prisoners in 1997 had intakes below the LRNI.