The incidence of vitamin D deficiency has increased in recent years, mainly in Europe. The consumption of processed mushrooms may play an important role in preventing diseases associated with vitamin D deficiency. We determined the effects of 2 kinds of freezing (blast, cryogenic), canning (mild and strong brine), and drying (air-drying, freeze-drying) on the retention of vitamin D2 and ergosterol in Agaricus bisporus. Fresh and processed A. bisporus mushrooms can be a good dietary source of vitamin D2. After 12 months of storage, canned mushrooms retained the largest amount of vitamin D2 and ergosterol, whereas the smallest amount was retained in dried mushrooms. Cryogenic freezing resulted in higher levels of vitamin D2, whereas ergosterol levels were higher using air-blast freezing. The drying method had a significant effect only on ergosterol levels, which were higher in the case of freeze-drying. Room temperature gave the best results for storing dried mushrooms. In canned mushrooms, the type of brine had an effect only on levels of vitamin D2; retention was higher using the strong brine. Retention of vitamin D2 was higher at cool temperatures, whereas room temperature resulted in higher retention of ergosterol in the canned products.