In one episode, a character asks if they saw the movie about those aliens that burst from people's chests (the Alien movies), and Paul Reiser says, "Only the first one." Reiser starred (and gets killed) in Aliens (1986), the second movie in this series.
Ursula Buffay (Lisa Kudrow), the waitress, is Phoebe Buffay's (Lisa Kudrow) twin sister, in Friends (1994). In one episode of Friends (1994), Fran and Jamie visit the coffee house and mistake Phoebe for Ursula.
In one episode, Paul and Jamie see Ursula after a long time of absence in the show. They ask her where she had been and she says "I've been hanging out with friends". Ursula is portrayed by Lisa Kudrow, who started starring in Friends (1994), thus her absence at Mad About You.
Paul and Jamie's daughter, Mabel, got her name from her grandma (played by Carol Burnett). When Paul and Jamie were looking for a name, Jamie's mother said to them, "Mothers always bring extra love" M.A.B.E.L.
Steve Buscemi appears in an episode in the first season which was inspired by an actual incident between himself and Paul Reiser. Before Buscemi began acting, he tried his hand at doing standup. One night, he bombed so badly that another comic had to take his place. That comic was Reiser and the episode pokes fun at the incident.
Paul Reiser's production company is called Nuance Productions, after a line in the first film he appeared in, Diner (1982): "You know what word I'm not comfortable with? Nuance. It's not a real word. Like "gesture". Gesture's a real word. With gesture you know where you stand. But nuance? I don't know. Maybe I'm wrong."