Purpose of study. The aim of this study is to evaluate the role of low intensity pulsed ultrasound, Exogen in the treatment of delayed and non unions. Methodology: We conducted a retrospective study of 292 patients who has had Exogen treatment for delayed and non union from 2005 to 2009. Patient's age, sex, associated co morbidities, smoking history, medications, type of fractures (open/closed), infection and site of fractures were sought for. 271 patients' data (228 delayed and 43 non unions) were available during the study with mean age of 53.5 yrs. Exogen therapy was initiated at 3–4 months for delayed unions and 6–12 months for non unions in 61 tibia (15 open); 31 femur (2 open); 20 scaphoid; 38 5th metatarsal; 31 ankle (2 open); 17 ulna (1 open); 15 radius (3 open); 29 humerus (2 open); 16 clavicles; 6 olecranon; 4 pilon (2 open) and 2 metacarpal fractures. Discussion. Union was achieved in 196 patients (72.3%) of which 11 (5.6%) were smokers. In 73 (26.9 %) patients union was not achieved of which 53 (72 %) were smokers. The mean healing timing after application of Exogen was 16 weeks for delayed union and 26.6 weeks for non union. 5 (31.2%) pt out of 16 in the DM group went into non union. Conclusion. In our study we found an accelerated union rate with Exogen therapy in delayed union, however smoking is a negative predictor for bone healing, which appears to be unaltered despite Exogen therapy(p=0.0032). Prescribing Exogen therapy early may be potentially beneficial to prevent an established non union