Background: Middle-aged and older adults often mistakenly underestimate the risk to which they are exposed when they engage in risky sexual behaviors. Furthermore, a reliable and valid measurement of the construct is necessary to capture its scope and meaning. Objective: To validate the structure of the Perceived Risk Scale for STIs in middle-aged and older adults, identify their perceived risk of STIs, and identify their relationship with some sociodemographic characteristics.Methods: The sample was composed of 295 middle-aged and older adults. A virtual online sampling was used. Males and females aged 50 years and older, sexually active in the last 12 months, were included. To measure the perceived risk of STIs, the scale of perceived risk for human immunodeficiency virus (HIV) was adapted, and a confirmatory factor analysis of the proposed three-factor structure was carried out.Results: The proposed structure of the scale was found to present acceptable adjustment rates (χ2 = 48.283, p˂.001; CFI = .962, RMSEA = .079, GFI = .963, TLI = .938). 28.1% of the participants presented low perceived risk; 46.8%, medium perceived risk; and 25.1%, high perceived risk. Association between marital status and perceived risk of STIs was identified. Conclusion: The Perceived Risk Scale for STIs is a reliable and valid instrument for captu-ring perceived risk of STIs in middle-aged and older adults. An appropriate measurement is considered important to accurately examine the relationship between perceived risk and behavior.