Objectives: We sought to compare the effectiveness of an antibiotic-impregnated bioabsorbable bone substitute (BBS, tobramycin-impregnated medical-grade calcium sulfate) with antibiotic-impregnated polymethylmethacrylate (PMMA) cement beads after surgical debridement in patients with chronic nonhematogenous osteomyelitis and/or infected nonunion. Design: A prospective, randomized clinical trial. Setting: A university-affiliated teaching hospital. Patients/Participants: Thirty patients requiring surgical treatment for chronic long bone infection or infected nonunion were included: BBS (15 patients, mean age 44.1 years) PMMA (15 patients, mean age 45.6 years). Intervention: Patients were randomized to receive either BBS or PMMA to the bone void created by surgical debridement. Main Outcome Measurements: Eradication of infection, new bone growth, rate of union, repeat operative procedures complications. Results: Patients were followed for a mean 38 months (range, 2460 months). One patient was lost to follow-up in each group. In the BBS group, infection was eradicated in 86% (12 of 14) of patients. Seven of eight patients achieved union of their nonunion, and five patients underwent seven further surgical procedures. In the PMMA group, infection was eradicated in 86% (12 of 14) of patients. Six of eight patients achieved union of their nonunion, and nine patients required 15 further surgical procedures. There were more reoperations in the PMMA group (15 versus seven, P = 0.04), and these procedures tended to be of greater magnitude. Conclusions: The results of this preliminary study suggest that, in the treatment of chronic osteomyelitis and infected nonunion, the use of an antibiotic-impregnated BBS is equivalent to standard surgical therapy in eradicating infection and that it may reduce the number of subsequent surgical procedures. A larger, definitive study on this topic is required.