On his return to Naples in 1978 he became rector of the major seminary until 1987, when he took up the post of dean of the S. Tommaso d'Aquino campus, where he had continued to teach.

He received his episcopal consecration on the following 13 May from Cardinal Michele Giordano, with Archbishops Luigi Diligenza and Antonio Ambrosanio serving as co-consecrators, in the Cathedral of Naples.

Upon the death of John Paul II on 2 April 2005, Vallini and all major Vatican officials automatically lost their positions.

Pope Benedict created him Cardinal-Deacon of S. Pier Damiani ai Monti di S. Paolo in the consistory of 24 March 2006.

[6] Distributing condoms in schools in the context of combating AIDS trivializes sexuality and education and must be fought by concerned parents, according to Vallini.

In an official statement, he responded to a decision by the civil authorities of the province of Rome to allow the distribution of condoms from vending machines in high schools (see religion and AIDS).