Purpose: To evaluate advantages and disadvantages of identical implants with internal or external connections. Materials and methods: One hundred and twenty patients with any type of edentulism (single tooth, partial and total edentulism), requiring one implant-supported prosthesis were randomly allocated in two equal groups to receive either implants with an external connection (EC) or implants of the same type with an internal connection (IC) (EZ Plus, MegaGen Implant, Gyeongbuk, South Korea), at four centres. Due to slight differences in implant design and components, IC implants were platformswitched while EC were not. Patients were followed for 5 years after initial loading. Outcome measures were prosthesis/implant failures, any complication, marginal bone level changes and clinician preference, assessed by blinded outcome assessors. Results: Sixty patients received 96 EC implants and 60 patients received 107 IC implants. Three patients dropped out with four EC implants and five patients with ten IC implants, but all remaining patients were followed up to 5-year post-loading. One prosthesis supported by EC implants and two by IC implants failed (P = 0.615, difference = -0.02, 95% CI: -0.08 to 0.04). One EC implant failed versus three IC implants in two patients (P = 0.615, difference = -0.02, 95% CI: -0.08 to 0.04). Ten complications occurred in 10 EC patients versus nine complications in 9 IC patients (P = 1.000, difference = 0.01, 95% CI: -0.13 to 0.15). There were no statistically significant differences for prosthesis and implant failures and complications between the different connection types. Five years after loading, there were no statistically significant differences in marginal bone level estimates between the two groups (difference = 0.14 mm, 95% CI: -0.28 to 0.56, P (ancova) = 0.505) and both groups lost bone from implant placement in a statistically significant way: 1.13 mm for the EC implants and 1.21 mm for the IC implants. Two operators had no preference and two preferred IC implants. Conclusions: Within the limitations given by the difference in neck design and platform switching between EC and IC implants, 5-year post-loading data did not show any statistically significant differences between the two connection types, therefore clinicians could choose whichever they preferred. Keywords: complication, dental implant, external connection, internal connection