Metcalfa pruinosa (Say) is an exotic pest introduced into Italy in the early 1980s. It is a polyphagous pest and can infest several plant species used in agriculture, forest, and urban systems. To control this pest, Neodryinus typhlocybae (Ashmead), a specialist parasitoid attacking young M. pruinosa instars, was introduced in Italy starting in 1987. From 1999 to 2001, the establishment of N. typhlocybae was evaluated and a sampling plan developed to estimate its cocoon population density. The spatial aggregation of the cocoons was analyzed by Taylor’s power law. The aggregation index ranged from 1.064 to 1.136 and a common value (b = 1.1) was estimated. Sequential sampling was shown to be the more practical and least time consuming sampling method. The peak of the parasitoid cocoon population at the end of July (26th to 30th week of the year) is a suitable period in northern Italy to monitor the activity of the parasitoid and to estimate the field parasitization. The potential of the sampling method is discussed, with the aim to evaluate the impact of the parasitoid on M. pruinosa populations.