The mishap occurred at the Kozhikode-Ramanattukara bypass.
The tourist bus, carrying 52 pilgrims, was returning to Idukki from the Kollur shrine in Karnataka when it overturned after hitting a lorry coming from the opposite direction, police said.
While 42 injured have been admitted to the Kozhikode Medical College Hospital and other hospitals here, seven others were treated for minor injuries, they said.