Police stated that the arrested person is a 26-year-old resident of Uppuveli area in Trincomalee.
Special attention has been paid to three persons in connection with the recovery of the hand grenade.
The police stated that statements have been recorded from the security division of the hospital and several others in this regard.
The grenade was found in a trash bin on the first floor of the Lanka Hospital in Narahenpita yesterday afternoon.
The grenade was taken out of the hospital premises by the Narahenpita Police and the STF Bomb Disposal Unit following a tip-off from the hospital security forces.
The hand grenade was designed to be activated with the help of a mosquito coil and police stated that the mosquito coil was not lit.
The Narahenpita Police and the Colombo Crimes Division have launched an investigation into the incident.
It is also reported that CCTV footage of the hospital is being further searched to find the suspects.
Investigations are underway to find out the motive behind bringing the bomb to the hospital premises.