Dineen made his debut with the Pittsburgh Penguins on December 23, 1988, earning no points in a 2–2 tie against the New Jersey Devils. On December 31, Dineen earned his first point as a Penguin, an assist on a goal by Mario Lemieux in an 8–6 victory. On February 14, Dineen scored his first goal with Pittsburgh against Jacques Cloutier of the Buffalo Sabres and added an assist in a 7–3 win. With the Penguins in 1988–89, Dineen played in 38 games, scoring a goal and three points. In the playoffs, Dineen added two assists in 11 games.