In the Pediatric Unit at Georgetown University Hospital, instead of seeing the usual team of doctors and nurses, patients were treated to a special visit from Elmo and Cookie Monster.
"It just reminds them it's okay to have fun and play and imagine," said Dr. Dorothy Richmond. "That's so important for a child."
Emily Clayton is 15-years-old and has spent much of her life in hospitals.
She was born with hirschsprung ganglionosis which is the lack of ganglion cells in her intestines, said Emily's mother Lea Clayton.
After a bowel transplant in 2005, Emily developed cancer. On Wednesday, she was slated to undergo chemotherapy.
But seeing the famous visitors "raised her spirits," she said.
Medical experts say visits like this can make a huge impact on pediatric patients. Some believe they can actually help speed up healing and recovery.
"They're a lot livelier and many times they're more cooperative with their treatment afterward because they just feel better," said Richmond.