The aim of this study was to assess changes in the horizontal dimension of the alveolar ridge using the autogenous bone block (ABB) or periosteal pocket flap (PPF) techniques prior to implant placement. This randomized trial study was conducted on 25 patients in need of horizontal bone augmentation who were randomly divided into two groups as follows: 13 underwent ridge augmentation with ABB in combination with allograft and collagen membrane, and 12 underwent ridge augmentation with the PPF technique. Radiographic examination via CBCT was conducted on all patients before and 26 weeks after the operation. Dimensional changes in the ridge width following surgery were measured within each group and also between the two groups in three regions: 0, 3, and 5 mm from the top of the alveolar crest. Eleven patients in the ABB group and all 12 patients in the PPF group successfully completed the study. Statistical analysis showed that the increase in alveolar ridge width in each group was significant, but the difference between the groups was not significant at any of the measured spots (0 mm from the crest, P = .25; 3 mm, P = .38; 5 mm, P = .73). However, more postoperative complications were observed with the ABB technique. According to the results of this study, there was no statistically significant difference between PPF and ABB techniques in terms of horizontal bone gain.