Background: Forearm shaft fractures are common in developing countries. Anatomical reduction of these fractures using plates and screws is considered an accepted treatment mode. Like other shaft fractures, this can be treated with intramedullary nails like square nails, Rush nails, and interlocking nails. This study evaluates radiological and functional treatment results using square nailing. Methods: A prospective study was conducted on 100 adult patients with diaphyseal forearm fractures over 3 years. Out of 100 patients, 68 were men, and 32 were women. Patients were followed up at 2 weeks, 6 weeks, 8 weeks, and then every 3 months till 1 to 1.5 years. We have used criteria described by Anderson et al. and the shortened version of the Disabilities of the Arm, Shoulder, and Hand (QuickDASH) score for functional evaluation of the patients. Results: Out of 100 patients, the union was achieved in 88 patients, while the rest 12 patients required re-surgery. 4 patients had delayed union, 4 patients developed an infection at the ulnar entry site, and 3 patients developed bursitis of olecranon bursa. Conclusion: Intramedullary nailing of both bone forearm shaft fractures using square nails can give satisfactory results in most cases, comparable with treatment by plates and screws, and provides an alternative, cost-effective treatment of both bone forearm shafts fractures with good cosmesis owing to small incisions. [ABSTRACT FROM AUTHOR]