[Purpose] The aims of our study were, 1. to assess pain, limitation of movement ability, and functionality in osteoarthritis patients scheduled to undergo total knee arthroplasty, 2. to determine if pain (Group 1) or function loss (Group 2) has a greater influence on the decision of patients to have surgery, and 3. to compare results between Group 1 and Group 2. [Subject and Methods] Fifty-five osteoarthritis patients classified as grades 3 and 4 according to the Kellgren-Lawrence system of classification were evaluated for preoperative pain intensity with the Visual Analogue Scale, knee flexion/extension range of movement with a clinical goniometer, and function with the Western Ontario and McMaster Universities Osteoarthritis Index. Patients were examined to reveal their reasons regarding the decision to undergo total knee arthroplasty (pain or function loss). [Results] The Visual Analog Scale scores at rest and during activity were 5.62 and 7.42, the knee flexion range of movement and extension limitation were 93.17° and −7.04°, and the Western Ontario and McMaster Universities Osteoarthritis Index value was 82.09. Regarding the decision to undergo surgery, 47.3% (n=26) of the knees were in Group 1, and 52.7% were in Group 2; the two groups were not significantly different. There were also no significant differences between the groups in Visual Analog Scale score during activity, the Western Ontario and McMaster Universities Osteoarthritis Index value, and knee flexion range of movement and extension limitation. The only statistically significant difference was found in the Visual Analog Scale score at rest in Group 1, which was significantly higher than that in Group 2. [Conclusion] Our results showed that osteoarthritis patients decided to undergo surgery only if all of the parameters were impaired significantly. Both pain and function loss have a similar impact on a patient’s decision to undergo surgery. We observed no significant difference in clinical and self-reported outcomes between patients who decided to undergo surgery due to pain or function loss.