Nowadays it seems that almost every successful television series winds up on the silver screen. For a while, every series from the '60s and '70s was being made into a film - from Mission Impossible to The Beverly Hillbillies.
Before that, in the early days of television, Hollywood refused to admit to its existence on screen. Television was seen as a competitor and no TV set was shown or mentioned.
So, what was the first television series to wind up on the cinema screen?
The earliest I can think of is The Quatermass Experiment from 1955. A Hammer Film adaptation of the BBC series that was itself an adaptation of a radio play. Admittedly, not a Hollywood film. Was there something earlier? I'm sure there must be.