There is growing concern that large Medicaid practices (LMPs) may be "Medicaid mills" in which low-quality care is provided. Based on survey data, this study sought to determine whether physicians who treat a disproportionate number of Medicaid patients are in fact operating mills. While practices with at least 30% Medicaid patients are a minority of all practices (15.8%), nearly 60% of all Medicaid patients receive care there. There is no evidence that LMPs can be characterized as Medicaid mills. Visit lengths are shorter in LMPs, but only by two minutes. Nor is there any widespread abuse of ancillary services, skimping on auxiliary staff, or excessive incomes. The LMP physicians, however, do tend to be older, to be trained in foreign medical schools, and to have fewer credentials, such as board certification.