Mushrooms accumulate arsenic (As), yet As concentrations, speciation, and localization in cultivated mushrooms across a large geographic distribution are unknown. We characterized 141 samples of nine species from markets in nine capital cities in China, with samples of Lentinula edodes, Pleurotus ostreatus, and Agaricus bisporus being analyzed for As speciation and localization. Total As concentrations ranged from 0.01 to 8.31 mg kg-1 dw, with A. bisporus (0.27-2.79 mg kg-1) containing the most As followed by P. ostreatus and L. edodes (0.04-8.31 and 0.12-2.58 mg kg-1). However, As in A. bisporus was mostly organic including nontoxic arsenobetaine, while P. ostreatus and L. edodes contained mainly inorganic As (iAs). On the basis of in situ imaging using LA-ICP-MS, As in L. edodes was localized to the surface coat of the cap, while As in P. ostreatus was localized to the junction of the pileus and stipe. When As speciation and daily mushroom consumption (1.37 g d-1 dw) are considered, daily mushroom consumption may result in elevated iAs exposure, with increased bladder and lung cancer rates up to 387 cases per 100000. Our study showed that market mushrooms could be a health risk to the general public so its production should be monitored.