London's Children's Hospital played host to a world-renowned expert on Tuesday, but he's not a doctor.

His specialty isn't even medicine in the conventional sense, but a field that helps to lift the spirits of young patients and their families - therapeutic clowning.

For seven-year-old Michael Gorbasew a visit from Ollie the Clown in his room at Children's Hospital is always special.

But it was Ollie's turn for a special visitor - Andre Poulie of the Theodora Foundation based in Geneva - a group dedicated to advancing the art and skill of therapeutic clowns.

"It's in memory of my mother whose name was Theodora. As a child I did a lot of silly things and ended up in hospital from time to time - one time fairly long - and she was there every day," Poulie explains.

The theraputic clown program has been at Children's Hosptial for 10 years. Last year alone, Ollie worked with more than 3,500 children.

It's funny business with a serious side, Ollie - whose real name is Ken Sperling, helps children through the challenges of being in hospital.

"Usually I use a lot of humour, laughter, slapstick, blow up balloons, magic, bubbles, anything. I use anything in the room," Sperling says.

Michael has leukemia and visits with Ollie help him to just be a kid.

His mom Fran Gorbasew says "I think laughter is really important, especially when you're going through something traumatic like this and it helps with healing. So he brings that into the room. He brings in laughter. He brings in happiness."

Michael adds "He paints me balloons, makes me laugh, smile."

Poulie is impressed by what he sees at Children's Hospital.

"What Ollie's doing has a lot in common with our work...clowning has different traditions. We're are more of the southern European, Latin one."

For Ollie, clowning is a full-time job supported through the Children's Health Foundation, and it's also a vocation.

Sperling says "I've got a dream job. It's wonderful."