This article analyses the contribution of public investment to economic growth in Southern Italy in the second half of the twentieth century (1951-2011). The Bai-Perron tests suggest that economic growth followed three distinct regimes: accelerated growth in the years 1951-1973 (average growth rate 5.3%); low growth in the period 1974-1995 (average growth rate 1.6%); zero growth on average after 1995. Using cointegration analysis, we find a positive effect of public investment on per unit of labour output of the Mezzogiorno in the whole period, 1951-2011. However, the estimates of the model show statistically significant parameters of public investment in the first regime, but not in the second regime, when economic growth is sustained by b...