The effects of leaking on the quality of modified-atmosphere-packed chilled minced meat pizza were studied. Capillary-like leaks of various sizes were made experimentally in the sealing area with tungsten threads of diameters 50 and 100 μm. Test packages were stored for 5 weeks at 5 °C (in darkness or under illumination) or at 10 °C in darkness and the microbial and sensory deterioration of pizzas packed in leaking packages was compared to that occurring in intact packages. The diameter of the capillary leakage was found to influence markedly the rate of deterioration of pizzas stored under all conditions. The higher storage temperature accelerated the deterioration of the quality of pizzas in all packages, but illumination increased the rate of deterioration especially in leaking packages. The colour indicator tested reacted to different leak sizes as anticipated and was shown to be reliable in leak detection.