The incident happened east of the Westbury station just after 11 a.m., when one train apparently rear-ended the other.
After LIRR officials inspected the rails, they determined there was no derailment, so no damage to the track and that should speed of the process of getting service moving again.
Two train operators, preliminarily identified as men in their 40s, were taken to Nassau University Medical Center with injuries not believed to be life threatening.
Three others refused hospitalization and were checked out at the scene.
LIRR suspended service between Mineola and Hicksville on the Port Jefferson and Ronkonkoma branches for a few hours, but service was partially restored by mid-afternoon. There was a near normal evening commute.