Purpose: To compare the effectiveness of two different techniques to lift the maxillary sinus via a crestal approach: the Summers versus the Cosci technique. Materials and methods: Fifteen partially edentulous patients missing bilaterally maxillary molars and/ or premolars, having 4 to 7 mm of residual crestal height and at least 5 mm thickness below the maxillary sinuses measured on CT scans, were randomised to have implants placed in sinuses crestally lifted according to the Cosci or the Summers techniques, with bone substitutes according to a split-mouth design. Implants were left to heal submerged for 6 months. Implants were loaded with acrylic provisional crowns/prostheses. Screw-retained definitive metal-ceramic prostheses were delivered 4 months after provisional loading. Outcome measures were: prosthesis and implant failures; any complications; operation time; operator preference; patient preference and peri-implant marginal bone level changes assessed by a blinded outcome assessor. All patients were followed to 3 years after implant loading. Results: Nineteen study implants were placed according to each technique. Three years after loading, 3 patients dropped out and no implant failed. No discomfort/complications occurred at sites treated with the Cosci technique, whereas 12 patients reported discomfort during the augmentation procedure at the side treated with the Summers technique; this was statistically significant (P = 0.0005). In one of these patients, a perforation of the sinus membrane occurred. Postoperatively, headache was reported by 9 patients and swelling occurred in 3 of these patients at the Summers treated sides. Statistically significant less time (9.7 mins, SD = 4.0, P < 0.001, 95% CI -11.9 to -7.5) was required to place implants according to the Cosci technique (33 versus 24 mins on average). The 2 operators and 14 out of 15 patients preferred the Cosci technique 1 month after surgery (P = 0.001), and 1 year after surgery (13 out of 15 patients, P = 0.007). The ceramic layer of one prosthesis of the Summers' group and one abutment screw of the Cosci's group loosened between 1 to 3 years post-loading. After 3 years, implants inserted according to the Cosci technique lost 1.39 mm of peri-implant bone versus 1.54 mm for the implants placed with the Summers technique. There were no statistically significant differences for marginal bone level changes between the two groups (difference 0.15 mm, 95% CI -0.11 to 0.41, P = 0.24). Conclusions: Both crestal sinus lift techniques produced successful results over a 3-year follow-up period, but the Cosci technique required less surgical time, determined less intra- and postoperative morbidity and was preferred by patients.