Knee osteoarthritis (KO) is an important health condition, affecting one third of people aged 65 years or more. Pain is the main cause of disability. Pain management in KO includes pharmacological and non-pharmacological modalities. Patient education, lifestyle changes, physical exercise, and physical agents are prescribed as a first approach for pain control. Laser therapy is part of many therapeutical protocols, with two forms: low-level laser therapy (LLLT) and high-intensity laser therapy (HILT). This paper aimed to stress the advantages of HILT based on a greater wavelength, higher energy delivery, and deeper tissue penetration. Research on 23 published trials revealed that the analgesic effect is rapid, cumulative, and long lasting. Compared to sham, to LLLT, or to other combinations of therapeutical modalities, HILT provided significantly better results on pain reduction and functional improvement. Ultrasound examination showed a reduction in intra-articular inflammation.