The effects of progressive resistance exercise (PRE) on the motor signs of Parkinson's disease have not been studied in controlled trials. The objective of the current trial was to compare 6-, 12-, 18-, and 24-month outcomes of patients with Parkinson's disease who received PRE with a stretching, balance, and strengthening exercise program. The authors conducted a randomized controlled trial between September 2007 and July 2011. Pairs of patients matched by sex and off-medication scores on the Unified Parkinson's Disease Rating Scale, motor subscale (UPDRS-III), were randomly assigned to the interventions with a 1:1 allocation ratio. The PRE group performed a weight-lifting program. The modified fitness counts (mFC) group performed a stretching, balance, and strengthening exercise program. Patients exercised 2 days per week for 24 months at a gym. A personal trainer directed both weekly sessions for the first 6 months and 1 weekly session after 6 months. The primary outcome was the off-medication UPDRS-III score. Patients were followed for 24 months at 6-month intervals. Of 51 patients, 20 in the PRE group and 18 in the mFC group completed the trial. At 24 months, the mean off-medication UPDRS-III score decreased more with PRE than with mFC (mean difference, -7.3 points; 95% confidence interval, -11.3 to -3.6; P<0.001). The PRE group had 10 adverse events, and the mFC group had 7 adverse events. PRE demonstrated a statistically and clinically significant reduction in UPDRS-III scores compared with mFC and is recommended as a useful adjunct therapy to improve Parkinsonian motor signs. © 2013 Movement Disorder Society.