Abstract Background Despite the achievements of previous research, caregiving assessments in severe mental illness should be crossculturally validated in order to define risk groups or to evaluate family work. This study reports on the psychometric properties of the European version of the Involvement Evaluation Questionnaire (IEQ-EU) in Portugal. Methods A Portuguese translation of the IEQ-EU was developed according to the 'European Psychiatric Services: Inputs Linked to Outcome Domains and Needs' (EPSILON) group guidelines. We then studied 194 caregivers who were related to patients with schizophrenia spectrum disorders in psychiatric outpatient services. All relatives were assessed using the IEQ-EU. In order to describe the corresponding patients' sample, the majority (n = 162) was evaluated with the World Health Organization Disability Assessment Schedule (WHO-DAS II); 108 patients were also assessed with the Brief Psychiatric Rating Scale (BPRS) and the Global Assessment of Functioning (GAF). Results The factor structure of the Portuguese version of the questionnaire was similar to the original; internal consistency was good, with Cronbach's α ranging from 0.71 to 0.87 in the IEQ-EU scales (total score and domains: tension, supervision, worrying, urging); test-retest reliability yielded intraclass correlation coefficients (ICCs) from 0.80 to 0.94, concerning the same scores. Ecological validity was confirmed. Most caregiving consequences were reported on the worrying domain of the IEQ-EU. Conclusions Validity and reliability of the Portuguese IEQ-EU translation were established. Specifically the four IEQ-EU subscale domains seem to be valid in Portugal.