Using some new techniques of panel cointegration analysis, this paper describes the long-run impact of digital capital on the aggregate performance of the US and EU-15 member countries. ICT is found to significantly impact on output levels without substantial cross-country variation when one adopts the dynamic extension of panel OLS (PDOLS). In this case, however, the long-run elasticity of factor inputs does not differ from the one estimated in the short-run. The time-series version of seemingly unrelated regression (DSUR) provides more plausible findings, showing a significant cross-countries heterogeneity. The effect of ICT on growth appears relevant - and higher than emerging from short-differences - for most economies but not for the EU largest countries.