In 1970, Josip Županov presented his Egalitarian Syndrome Theory (EST) to account for the country’s suboptimal socioeconomic development. The theory was operationalized only recently (Štulhofer and Burić, 2015), which enabled an assessment of the persistence of egalitarian syndrome, as well as the testing of its hypothesized (negative) association with indicators of social development. Using data from a 2015 national probability survey, this study aimed to provide additional validation of the multidimensional measure of the egalitarian syndrome, including age and gender invariance testing, as well as to explore the hypothesized negative association with county-level development indices. The findings support Županov’s theoretical assumptions. Rural vs. urban residence, education and occupation, but not participants’ age, were significant predictors of the support for egalitarian syndrome. Significant negative associations were observed between the acceptance of values associated with the egalitarian syndrome and county-level development and competitiveness scores, GDP and early entrepreneurial activity. Although our study was not designed to test the causal relationship between radical egalitarianism and socioeconomic development, the findings suggest that the widespread prevalence of the egalitarian syndrome may be a problem for the country’s socio-economic development.