Objectives. To assess the psychometric properties of a scale to measure the satisfaction of individuals seeking services at outpatient clinics (ESCOMA) in public healthcare centers in Peru. Materials and Methods. We carried out a study based on a dataset from Questionnaire 1 of the National Health Users Satisfaction Survey (ENSUSALUD) 2016. ENSUSALUD applied an initial scale of 19 items constructed based on bibliographic review, expert judgment and a pilot study. We first performed an exploratory factor analysis (EFA) in two random subsamples to assess the scale’s internal structure. We then developed a confirmatory factor analysis (CFA) using robust maximum likelihood estimation. Lastly, we analyzed measurement invariance and assessed reliability using McDonald’s Omega Coefficient (ω). Results: We randomly divided 13,814 observations into two subsamples for the EFA. Based on this analysis, we selected a best-fitting CFA model, which comprised three factors and 18 items. We found acceptable goodness-of-fit indices for the CFA (CFI = 0.945, TLI = 0.937, SRMR = 0.036). The three resulting factors were a) administrative processes, b) infrastructure and c) medical care. We found strong invariance for age, sex, educational level and area of residence, and partial invariance for type of institution. All reliability coefficients indicated adequate fit (0.86<ω<0.92). Conclusions. The ESCOMA demonstrates validity, reliability, and measurement invariance at different levels of care in a nationally representative Peruvian sample.