The Simpsons might be the longest running animated series.It is in it's 18th season having started in 1989.I did a quck check on the Guinness website but couldn't find a listing for animated shows.
Coronation Street,Eastenders and Emmerdale have all been on air for longer than 18 years.
Guinness lists as longest running drama a programme called Guiding Light which began in June 1952.