The objective of this study was to compare the results of calcaneal lengthening and Dennyson–Fulford extra-articular subtalar arthrodesis operations performed in patients with flexible pes planovalgus owing to various etiologies and to compare their effectiveness in realigning the foot. Two patient groups were retrospectively formed out of the patients in whom calcaneal lengthening (25 feet of 13 patients) and subtalar extra-articular arthrodesis (27 feet of 15 patients) operations were performed. The modified Evans technique for the calcaneal lengthening operation and the Dennyson–Fulford technique for the subtalar extra-articular arthrodesis operation were applied. Any special criterion to choose the indication was not considered. The main indication for the surgery was pain during daily routine activities in both groups. The patients were evaluated preoperatively and during the last visit, both clinically and radiographically. The groups were homogenous for sex and mean age for the process, but in the subtalar extra-articular arthrodesis group, the deformity was more severe in some parameters, mean follow-up period was significantly longer and neurologic etiologies were more dominant. Anteroposterior talocalcaneal and talonavicular angles were worse in the subtalar extra-articular arthrodesis group preoperatively (P<0.05). Both groups showed significant correction (P<0.05) in all parameters postoperatively. In the last visit, lateral talocalcaneal, anteroposterior, and lateral talonavicular angles were worse in the calcaneal lengthening group (P<0.05) and calcaneal pitch angle was worse in the subtalar extra-articular arthrodesis group (P<0.05). Both groups showed significant clinical correction (P<0.05) in all parameters postoperatively, but there was no significant difference between the groups during the last visit in terms of total clinical scores (P>0.05). Pain, the parameter that was the main indication for surgery, was eliminated in all patients except for one in the calcaneal lengthening group. The evaluation of the effectiveness of the surgical technique on the results made by performing repeated measures from general linear models showed significantly better correction in anteroposterior and lateral talocalcaneal angles, anteroposterior and lateral talonavicular angles, and medial longitudinal arc angle in the subtalar extra-articular arthrodesis group (P<0.05). In conclusion, in this study group, the subtalar extra-articular arthrodesis technique was superior in talocalcaneonavicular joint complex reduction and medial longitudinal arc reconstruction in the surgical treatment of flexible pes planovalgus, and calcaneal lengthening provided better correction of calcaneal equinus. Therefore, it is better to use the calcaneal lengthening technique in mild or moderate deformities because of its physiological advantages, and subtalar extra-articular arthrodesis technique in severe and/or rigid deformities because of its superior potential to correct the deformity and stabilize the foot in the corrected position.