Defence lawyer Barry Roux read excerpts from a psychologist's report that said the double-amputee runner is suffering depression and post-traumatic stress disorder and "his condition is likely to worsen" if professional treatment for those conditions is halted.
The report was compiled during a 30-day observation period at a state psychiatric hospital. A report was also compiled by three psychiatrists.
The experts concluded Pistorius was not mentally ill when he shot Ms Steenkamp through a closed toilet door on February 14, 2013.
The court-ordered evaluation occurred after a psychiatrist testifying for the defence said Pistorius was suffering from an anxiety disorder that may have influenced his actions on the night he killed Ms Steenkamp.
At times during his trial, Pistorius has wailed and retched in apparent distress, particularly during graphic testimony about the shooting and also when the athlete was on the witness stand.
At other times, he has been calm and taken notes.
Chief prosecutor Gerrie Nel has suggested Pistorius has feigned distress.
The trial continues.