The present study investigated the structure of the Spanish version of the Iowa-Netherlands Comparison Orientation Measure (INCOM-E), an 11-item measure that assesses individual differences in social comparison orientation (SCO), i.e., the extent to which people compare themselves with others. Data came from samples from Spain (n = 1,133) and Chile (n = 2,757). Confirmatory Factor Analyses and Mokken Scale Analyses supported in both samples not the assumed two-factor structure, but a single factor structure, consisting of eight items. The resulting eight-item version of the INCOM- E was reliable in both samples, according the Gutmann's lambda-2 (.82 in Spain and .83 in Chile), and correlated very strongly with the full-length INCOM-E (.93 in Spain and .97 in Chile). In both samples, there were significant sex differences, ps < .001 with small effect sizes, ƞ2 in both samples = .01,but in the Spanish sample women scored higher, and in the Chilean sample men scored higher in SCO. The relationship with age was negative and significant (ps < .001) in both samples, albeit small (r = .22 in Spain and .13 in Chile) Based on the present research, it is advised to use the shortened eight-item version of the INCOM-E in Spanish speaking countries.