Sweet's syndrome is reportedly associated with preceding nontuberculous mycobacterial infections (NTMIs). Here, we report on a systemic Mycobacterium intracellulare infection in a patient on corticoid therapy for Sweet's syndrome. Literature searches show that 69.1% of patients with Sweet's syndrome and NTMIs developed this syndrome later than NTMIs and 89.3% of them developed during the clinical course of a rapidly growing mycobacterial infection. The residual cases were associated with slow-growing mycobacteria (14.3%), but only three cases of Mycobacterium avium complex (MAC) infections before the onset of Sweet's syndrome have been reported, and all of them were caused by disseminated MAC disease. One of these cases developed during corticoid therapy for Sweet's syndrome, while another case had underlying diabetes mellitus. Hence, the occurrence of systemic MAC disease may be an inevitable consequence of long-term steroid use and underlying diseases. Literature searches also show that cervical lymphadenitis was a predominant symptom in NTMIs (90.5%). The present case did not have cervical lymphadenitis although the previously reported MAC cases did experience it. Therefore, lymphadenitis from NTMIs may be related to the pathogenesis of Sweet's syndrome. Hence, should a patient have systemic infection without lymphadenitis, it will be more difficult to clinically confirm that MAC disease is a predisposing factor for Sweet's syndrome.