Purpose: To compare the prosthetic outcomes of screw-retained monolithic zirconia (Zr) single crowns supported by either narrow-diameter (3.3 mm) or standard-diameter (4.1 mm) tissue-level titanium-zirconia (TiZr) implants in posterior sites. Materials and Methods: A total of 18 participants, each with a missing molar or premolar tooth requiring an implantsupported single crown, were randomly assigned to either the test or control group. All participants received screwretained monolithic Zr single crowns supported by single tissue-level TiZr implants. Test group participants received narrow-diameter implants (3.3 mm), whereas control group participants received standard-diameter implants (4.1 mm). A modified version of the United States Public Health Service (USPHS) criteria was used to assess the prosthetic outcome across 12 parameters after 1 year of function. Data were analyzed descriptively, and statistical analysis was performed using a statistical software (SPSS, Version 28.0; IBM) with the level of significance set at P < .05. Results: Of the 18 single crowns delivered, 16 were available for review at the 1-year follow-up, including 7 in the test group and 9 in the control group. Patient characteristics and crown site distribution were similar, with no significant differences observed between the two groups (chi-square test; P < .05). There were no crown failures, meaning a crown survival rate of 100% was achieved after 1 year. The prosthetic outcome based on USPHS criteria was comparable between the two groups with no significant differences observed (chi-square test; P < .05). There were 19 prosthetic events in total (10 in the test group and 9 in the control group), with no significant differences between the groups (chi-square test; P < .05). Loss of proximal contact was the dominant event, with a total of eight events (three in the test group and five in the control group). Patient satisfaction after 1 year was high in both treatment groups, with no significant differences detected. Conclusions: Screw-retained monolithic Zr single crowns supported by either narrow- or standard-diameter tissue-level TiZr implants in posterior sites have comparable prosthetic outcomes after 1 year. Long-term results from well-designed trials are still needed to validate the findings of the present study.