Inflammatory changes in the peri-implant tissues may lead to peri-implantitis and bone loss. Prostaglandin E2 has been shown to have proinflammatory effects on peri-implant tissues, including mediation of bone resorption. The aim of this study was to assess prostaglandin E2 levels in implant crevicular fluid and the possibility of using this method in diagnosing peri-implant mucositis. Twenty-four dental implants with 3 mm or greater probing depths comprised the test group and another 24 implants with probing depths less than 3 mm served as the control group. Plaque index (PI), gingival index (GI), and probing pocket depths (PPD) were recorded. Implant crevicular fluid was obtained by collection onto periopapers. Then, prostaglandin E2 levels were evaluated using a commercially available enzyme immuno-assay kit. PI, GI, PPD, and implant crevicular fluid (ICF) levels of prostaglandin E2 were found to be statistically significantly higher in the test group (P < 0.05). In the test group, gingival index and probing depths were found to be statistically significantly related with ICF prostaglandin E2 levels (P < 0.05). In the control group, there was no statistically significant positive correlation between clinical parameters and ICF prostaglandin E2 levels (P > 0.05). It may be speculated that biochemical tests, such as the detection of prostaglandin E2 levels in the crevicular fluid are useful diagnostic methods for the maintenance of functional dental implants.