Polka Dot Door was a children's television series produced and broadcast by TVOntario from 1971 until 1993. The music was played, written, and directed by Canadian pianist John Arpin.

The show, which aired Monday to Friday, was set in a large playhouse. Each episode had two human hosts, always one man and one woman, although there were many different human hosts over the course of the series. The same pair would host the show for a week; the next week would bring a new pair of hosts.

The hosts would lead children in songs and stories, and interact with stuffed animal characters Humpty, Dumpty, Marigold and Bear. They would often peer through the Polka Dot Door to witness a video of some sort, showing, for instance, how crayons are made. They would also visit Storytime Mouse, who would emerge from a tall clock to help the hosts tell the time. Often the show would feature the music director John Arpin as well as musicians such as Peter Appleyard and Henry Cuesta for a round of songs.

Hosts of Polka Dot Door included Denis Simpson, Gloria Reuben, Tonya Lee Williams, Taborah Johnson, Cindy Cook, Catherine Bruhier, Rex Hagon, Sherry Miller, Johnie Chase, Nerene Virgin and Nina Keogh. In the show's first decade the most frequent host was Alex Laurier.

Each day's episode had a particular theme. On "Imagination Day", the character Polkaroo appeared. The actor playing Polkaroo donned a tall, green plush costume that resembled a kangaroo. In its mended, yellow and multi-coloured polka-dot muumuu, the creature never spoke other than the occasional exclamation of its own name. Polkaroo appeared only to one host while the other was away, performing a pantomime whose meaning was guessed by the audience. The missing host would return upon Polkaroo's departure, habitually exclaiming, "Polkaroo was here?!? And I missed him again?!?" (Although there is a common belief that the absent host was in the Polkaroo costume, Polkaroo was in fact played by another actor.)

Because of the irony laden in this sentence, Polkaroo has become something of a cultural icon to the generation raised on Polka Dot Door, and the catchphrase "Aw, I missed him again" may often be employed for humorous effect.

Polkaroo generally appeared once a week in the show's early years, although due to the character's popularity he began appearing more frequently toward the end of the show's run. In the late 1990s, TVOntario capitalized on the success of Polkaroo by placing him and the other animal characters in a new series, Polka Dot Shorts.