The aim of the present randomized split-mouth clinical trial was to compare plateletrich plasma (PRP) combined with a demineralized freeze-dried bone allograft (DFDBA) to DFDBA with a saline solution in the treatment of noncontained human periodontal intrabony defects. Forty-eight noncontained interproximal intrabony defects in 24 healthy nonsmoking patients diagnosed with chronic periodontitis were randomly assigned to the test group (PRP/DFDBA) or the control group (DFDBA/saline). Clinical (probing pocket depth, clinical attachment level [CAL], and gingival recession [REC]) and radiographic (bone fill, defect resolution, and alveolar crest resorption) measurements were made at baseline and at a 12-month evaluation. Compared with baseline, 12-month results indicated that both treatment modalities resulted in significant changes in all clinical and radiographic parameters. However, the test group exhibited statistically significantly greater changes compared with the control group in CAL (3.15 ± 0.50 versus 2.40 ± 0.61 mm), REC (0.54 ± 0.59 versus 1.23 ± 0.47 mm), bone fill (3.02 ± 0.50 versus 2.37 ± 0.47 mm), and defect resolution (3.29 ± 0.53 versus 2.69 ± 0.38 mm). Findings indicate that a combination of PRP and DFDBA is more effective than DFDBA with saline for the treatment of noncontained intrabony defects.