The present study explores the long‐term changes (1971–2001) in the socio‐economic structure of a monocentric Mediterranean urban region (Rome's province, central Italy) undergoing moderately polycentric development. Descriptive and correlation statistics and a multiway factor analysis (MFA) have been used to analyse the spatio‐temporal evolution of 24 socio‐economic indicators made available at the urban district/municipal scale. The socio‐economic disparities observed along the urban‐rural gradient in 1971 decreased only moderately in 2001. The MFA clearly separates urban districts from suburban municipalities in both 1971 and 2001. Results indicate that exurban development has impacted only partly Rome's urban form which remained mainly compact and dense with persisting socio‐economic gaps between urban and suburban areas. The paper discusses the partial failure of Rome's master plan to promote a really polycentric development and a new, more sustainable, urban form.