The measurement invariance of the Experiences in Close Relationships (ECR) questionnaire was investigated across four samples of non-clinical subjects (N = 222), dermatological patients (N = 458), psychiatric inpatients (N = 156), and patients with drug-resistant epilepsy (N = 101). The results provided evidence of configural, metric, and scalar invariance across groups. Overall, our findings provide further support to the reliability and validity of the ECR.