Nontuberculous mycobacterial (NTM) infections are on the rise and often cause skin diseases that are misdiagnosed. The authors present three cases of atypical mycobacterial infections in insulin-dependent diabetics occurring in sites of subcutaneous insulin injections. One of the patients was vitamin D deficient at the time of infection with NTM. The history and clinical presentation of the cases are presented; pathogenesis and treatment are discussed in conjunction with the correlation of mycobacterial disease susceptibility with vitamin D deficiency.