Paramedics say they were called to the area of Eglinton Avenue West and Scarlett Road shortly before 2 p.m.
The three patients were trapped and had to be extricated.
An elderly woman inside a car suffered a lower-leg fracture in the crash.
The driver of the other vehicle was a man in his 80s. He suffered chest and facial injuries. His passenger was a woman in her 70s. She suffered a fractured femur.
Toronto police reported that Scarlett Road was closed between Eglinton Avenue West and Larose Avenue for the ensuing investigation.
The TTC reported that buses on its 79 Scarlett Road and 73 B Royal York routes were diverting as a result of the road closure.