Purpose: This cross-sectional study aimed to analyze the relation between peri-implant soft tissue biotype (STB) and different levels of peri-implantitis severity, and to identify the possible risk indicators that affect the severity of peri-implantitis with regard to STB around dental implants. Materials and Methods: Eighty-seven patients with 229 implants were diagnosed with peri-implantitis and recruited to the study. Clinical and radiographic parameters including Plaque Index (PI), probing depth (PD), bleeding on probing (BOP), gingival/mucosal recession (GR/MR), clinical attachment level (CAL), and marginal bone loss (BL) were analyzed. The periodontal status was assessed, and the levels of peri-implantitis severity were defined. These parameters were compared among the peri-implant STB groups (thick and thin biotype). To evaluate the effect of possible risk indicators on the levels of severity of peri-implantitis, univariate and multivariate logistic regression analyses were conducted for thick and thin biotype groups. Results: The mean values of BOP, MR, CAL, and marginal BL were significantly lower for the thick group compared with the thin group (P < .05). For PI and PD values, no significant differences were found between the groups (P > .05). Moreover, multivariate analysis revealed statistically significant associations between peri-implantitis severity and the risk indicators of maintenance therapy compliance and current periodontitis for the thin group (P < .05). Conclusion: The thin biotype could be more prone to an increase in the severity of peri-implantitis. Maintenance therapy compliance and current periodontitis could be important risk indicators that affect the progression of the severity of peri-implantitis for implants where keratinized mucosa is thin or absent.