Purpose: The purpose of the present study was to compare the clinical and radiographic outcomes of single implants immediately placed and restored with two different implant-abutment connections. Materials and Methods: Forty subjects requiring single maxillary premolar replacement were consecutively included in this study and prospectively followed for 12 months. One implant was placed at the time of tooth extraction and immediately restored in each patient. Subjects were randomly selected to receive either prosthetic abutments with a Morse taper connection and a platform switch (test group) or conventional abutments with an internal connection and a matching diameter (control group). A provisional screw-retained crown was positioned and adjusted for nonfunctional loading within 24 hours. Four months later, the definitive crowns were delivered. Periodontal parameters and clinical and radiographic measurements of soft and hard tissue levels were recorded at the moment of prosthesis placement and at 4 and 12 months afterward. Means of the two groups were compared using paired and independent-sample t tests (P = .05). Results: Of the 40 patients recruited, 38 (24 women and 14 men) completed the study. No implants were lost in the control group, whereas one implant failed in the test group. At the 12-month examination, no statistically significant differences were seen between the two groups for periodontal parameters, marginal soft tissue level change, or papilla height (P > .05), but greater marginal bone loss was observed at the control sites (0.51 ± 0.24 mm) compared to the test sites (0.2 ± 0.17 mm) (P = .0004). Conclusion: Although the control group demonstrated a slight increase in marginal bone loss compared to the test group, the peri-implant soft tissues were very stable with both types of implant-abutment connection after 12 months of loading. Keywords: immediate implants, marginal bone loss, Morse taper connection, platform switching, single-tooth implant restoration