Background: The aim of this study is to examine the preoperative and postoperative forearm compartment pressures in patients treated operatively for Gartland type III extension type supracondyler humerus fractures and understand the course of these values over postoperative period. Methods: Deep volar compartment pressure of 31 patients were measured in the proximal one third of the forearm preoperatively, and measurements were continued every 4 hours for the first 24 hours after the operation with a catheter. Type of the reduction technique (open reduction vs. closed reduction), duration of surgery, the time from the injury to surgery were all evaluated. Results: In the measurements made immediately after the operation (0 h), a sudden increase in the compartment pressure was detected in all patients (15.0 +/- 5.9 to 27.9 +/- 7.5 mm Hg) independent of the reduction technique and gradually decreased over time. The mean compartment pressure at the 12th hour postoperatively was higher in the open reduction group than in the CR group (24.5 +/- 3.4, 20.7 +/- 6.7 mm Hg, respectively) (P=0.044). The mean preoperative compartment pressure was 17.7 +/- 5.8 mm Hg in patients with a time from injury to surgery longer than 12 hours, and 12.4 +/- 4.8 mm Hg in patients with 12 hours or less (P=0.006). The postoperative 0-, 12-, and 20-hour pressure values were higher in the >1 hour operation time group than in the <= 1 hour group and the differences were statistically significant (P=0.046, 0.016, and 0.032, respectively). Conclusions: In pediatric supracondylar humeral fractures, those who underwent open reduction had higher preoperative and postoperative compartment pressures. The reduction attempt was found to be a factor that increased the compartment pressure and after the operation, the compartment pressure values decrease gradually. Prolonged operative time (>1 h) and increased time from injury to operative fixation (>12 h) were associated with higher compartment pressures.