Diarrhea is a common problem in acquired immunodeficiency syndrome (AIDS). Aside from noninfectious causes, such as AIDS enteropathy and drug-induced diarrhea, the most common causes are opportunistic infections (OI). Disseminated Mycobacterium avium complex (MAC) is the most common OI with an incidence of 20% per year. There has been a dramatic decline in the incidence of disseminated MAC since the advent of highly active antiretroviral therapy (HAART). Clinicians must be familiar with the causes of diarrhea in AIDS to ensure timely institution of appropriate interventions. A fifty year old male with AIDS and CD4 count of three presented to the hospital with fever, encephalopathy, and failure to thrive. He was found to be septic with a urinary tract infection and bacteremia secondary to Escherichia coli, as well as Epstein-Barr virus (EBV) encephalitis. His hospital course was complicated by pancytopenia, and a bone marrow (BM) biopsy was performed due to concern for lymphoma in the setting of a positive EBV serology. Two weeks into hospitalization, he was resumed on his prior regimen of HAART, which included Ritonavir, Atazanavir, Emtricitabine and Tenofovir. One week later, he developed profuse, watery diarrhea. Stool studies were sent and while initially only positive for norovirus, two days later, acid-fast bacilli was also isolated. He began a regimen of Azithromycin, Isoniazid, Moxifloxacin, and Ethambutol to cover for both MAC and M. tuberculosis. His BM biopsy and blood cultures later resulted and were positive for MAC, confirming the diagnosis of disseminated MAC. Before HAART, diarrhea, which increases in frequency and severity as immune function declines, afflicted 40% to 80% of AIDS patients. With the initiation of HAART in a person with severe AIDS however, the risk of immune reconstitution inflammatory syndrome (IRIS) is significant and needs to be considered. Given the timing of this patient's diarrhea after resuming HAART, he most likely developed disseminated MAC secondary to IRIS. Although this patient initially tested positive for norovirus, which by itself would explain his diarrhea, comprehensive work-up led to the diagnosis of diarrhea secondary to disseminated MAC, and in turn, appropriate treatment. In an immunocompromised patient, multiple pathogens may be playing a role, and concomitant disease must always be considered.