Abstract: Haemophilus influenzae, a gram-negative pleomorphic bacillus, is a well- recognized pathogen in children. In recent years, it is increasingly recognized as an opportunistic pathogen in adults predominantly causing bacteremia, pneumonia, or meningitis. Impaired humoral immunity is a major factor in the development of more invasive infections. An extensive review of the literature reveals that it is infrequently identified as the etiologic agent of septic arthritis in adults. Initial management of septic arthritis includes surgical drainage and antibiotic therapy. We present a case of septic arthritis due to H influenzae serotype f in a patient with Waldenström macroglobulinemia. After surgical drainage and 3 weeks of antibiotic therapy, the patient resumed normal activity and has continued to do well after 1 year of follow-up. Physicians must be mindful of this invasive pathogen’s role in septic arthritis and the need for immediate surgical intervention and antibiotic administration so as to decrease associated morbidity and mortality.