The Hall of Fame center opened up on the procedure he had back in March ... explaining he was forced to take action following a routine prostate cancer screening that showed a rise in his PSA scores.

A second appointment confirmed Mourning had a Gleason score of eight ... which is a high grade of prostate cancer.

Prior to the medical discovery, Mourning said he felt in pristine condition.

"I was in shock," Mourning told ESPN. "I can't tell you enough about how well my body felt. I was in top-notch shape -- running sprints, strong."

Thankfully, the disease did not spread beyond the prostate ... and the cancer was surgically removed.

Mourning -- who is currently recovering from the procedure -- is calling on men to monitor their health more ... especially since prostate cancer is the second-leading cause of cancer among males.

"What scares me about this disease is that there are so many men walking around feeling great and have that cancer in them and they don't know it," the 54-year-old said.

"Unfortunately, as men, we don't like to go to the doctor, but this is the only way to find out what's going on in your body."

Mourning added ... "Prostate and even colon cancer are silent killers and many men won't get those diagnosis until it's too late."

This isn't the first health scare for Mourning -- back in 2003, he dealt with a life-threatening kidney disease ... and received a transplant from his cousin, who is a former U.S. Marine.

Mourning was the 2nd overall pick out of the 1992 NBA Draft ... and played most of his 15-year career with the Miami Heat.