Clostridium tertium has historically been regarded as nonpathogenic, and its implication as the primary microbe in infectious etiologies remains unclear. Although there have been several reports of C tertium isolated from blood, tissue, and other specimens, largely this population has consisted of patients with neutropenia, hematologic malignancies, or gastrointestinal disorders. Here we describe a case of a 39-year-old nonimmunocompromised man with a history of type 1 diabetes mellitus and intravenous drug use who presented to our institution with a necrotizing soft tissue infection involving his right upper extremity. The infection had developed after the patient had injected methamphetamines. At surgery, tissue was obtained for Gram stain and culture, yielding C tertium, after an initial misidentification as Lactobacillus species. After undergoing extensive surgical debridement and treatment with an appropriate antibiotic regimen, the patient was able to be discharged home with retained function of his extremity. Although not common, infections involving C tertium can produce severe, potentially life- and limb-threatening disease processes, which may require aggressive therapy even in the nonimmunocompromised patient.