Purpose: To compare the effectiveness of immediate post-extractive single implants with delayed implants placed in preserved sockets after 4 months of healing. Implants that achieved an insertion torque of at least 35 Ncm were immediately non-occlusally loaded. Materials and methods: Just after tooth extraction, and in the presence of less than 4 mm of vertical loss of the buccal bone in relation to the palatal wall, 50 patients requiring a single immediate post-extractive implant in the maxilla from second to second premolar were randomly allocated for either immediate implant placement (immediate group; 25 patients) or for socket preservation using an algae-derived (phycogenic) bone substitute, covered by a resorbable collagen barrier (delayed group; 25 patients), according to a parallel group design in one centre. Bone-to-implant gaps were filled with an algae-derived bone substitute. Four months after socket preservation, delayed implants were placed. Implants inserted with an insertion torque of at least 35 Ncm were immediately loaded with non-occluding provisional single crowns, then replaced, after 4 months, by definitive crowns. Patients were followed up to 1 year after loading. Outcome measures were implant failures, complications, aesthetics assessed using the pink esthetic score (PES), peri-implant marginal bone level changes and patient satisfaction, recorded by blinded assessors. Results: Nine (36%) implants were not immediately loaded in the immediate group versus 19 (76%) implants in the delayed placement group, because an insertion torque superior to 35 Ncm could not be obtained, the difference being statistically significant (difference = - 0.40, 95% CI: -0.652 to -0.148, P = 0.010). Two patients dropped out 4 months after loading in the delayed group versus none in the immediate group. Two implants failed in the immediate group (8%) versus none in the delayed group, with the difference showing no statistical significance (considering 25 and 23 patients, the difference in proportions was 8% favouring the delayed group, 95% CI: -8.4 to 26.0, P = 0.490). Three minor complications occurred in the immediate group and two in the delayed group, and this was not statistically significant (considering 25 and 23 patients, the difference in proportions was 3.3% favouring the delayed group, 95% CI: -18.2 to 24.0, P = 1.000). At delivery of definitive crowns, 4 months after loading, the mean aesthetic score was 12.42 and 12.28 in the immediate and delayed groups, respectively. At 1 year after loading, the mean aesthetic score was 12.78 and 12.22 in the immediate and delayed groups, respectively. There were no statistically significant differences at 4 months (P = 0.666) and at 1 year (P = 0.090). Marginal bone levels at implant insertion (after bone grafting) were 0.01 mm for immediate and 0.06 mm for delayed implants, which showed a statistically significant difference (mean difference = - 0.04; 95% CI: -0.08 to -0.01; P = 0.009). One year after loading, patients of the immediate group lost on average 0.13 mm marginal bone and those in the delayed group lost 0.19 mm, however the difference was not statistically significant (mean difference = 0.05; 95% CI: -0.002 to 0.110; P = 0.06). All patients were fully satisfied, both for function and aesthetics, and would undergo the same procedure again at 4 months as well as at 1 year after loading. Conclusions: No significant differences were observed between the two procedures, although the only two implant failures were for immediate post-extractive implants. It seems more difficult to obtain an implant insertion torque superior to 35 Ncm in sockets preserved with algae-derived bone substitute after a 4-month healing period than at immediate post-extractive sites. Keywords: delayed implantation, immediate loading, immediate post-extractive implants, single implants, socket preservation