Objective: Periodontal and peri-implant diseases are similar and can result in the destruction of supporting tissues. Although clinical indexes and radiological examinations are the standardized method of diagnosis, the literature is concerned with the diagnostic potential of gingival crevicular fluid (GCF) and peri-implant sulcus fluid (PISF). This cross-sectional study aimed to evaluate the effect of periodontal healthy and diseased conditions on the volume of GCF and PISF. Methods: Our study included GCF and PISF collected from 40 patients who have at least 3 dental implant [26 periodontally healthy (H), 27 gingivitis (G), 26 periodontitis (P); 26 healthy implants (HI), 27 peri-implant mucositis (PM), and 27 peri-implantitis (PI)]. The inclusion criteria for healthy teeth and implants were absence of bone loss around the teeth or implant and bleeding on probing (BOP)(-); for peri-implantitis, radiologic bone loss (RBL)>1 mm around the implant and BOP(+); for peri-implant mucositis RBL1 mm around the implant and BOP(+); for gingivitis with no RBL and attachment loss, and BOP(+); for periodontitis attachment loss and BOP(+). In the periodontal examination of the patients, the periodontal pocket depth (PPD), gingival index (GI), plaque index (PI), and clinical attachment level (CAL) were measured by a calibrated periodontist. GCF and PISF samples were collected and measured in a PERIOTRON 8000 device and the results were converted into volume by third party software. The periodontal parameters and GCF and PISF volumes were compared between groups using SPSS statistical analysis software v.24. Results: Although we found a statistically significant difference between the G and P, PM and PI, H and P, and HI and PI groups (p0.005), no statistically significant difference was found between the HI and PM, and H and G groups (p>0.005). In addition, there was a correlation between GCF volume and CAL and RBL in the PI and P groups. Conclusions: Despite the limitations of our study, it can be said that GCF volume increases in the presence of periodontal and peri-implant disease especially in patients with periodontitis and peri-implantitis, and that PISF and GCF can be used in addition to radiological examinations during the differential diagnosis of peri-implant diseases. Schlagwörter: periodontal disease, peri-implant disease, gingival crevicular fluid, peri-implant sulcus fluid