The birthday party is taking place in a private room in the hospital, reported Aceshowbiz.
A source said, "It's something very small and very short but will make him feel amazing. Then Khloe will be with him for the rest of the day."
"It's just a very small group of people because Lamar cannot handle too much stimulus, but the doctors are allowing a small group for a short time on his birthday," the source added.
A few Los Angeles Clippers players and Lamar's NBA trainer of 15 years would also come to the hospital to celebrate his birthday.