Significance. Researchers have separately examined the effects of resistance training and aerobic exercise on various measures of fitness in adults with MS. The purpose of the study was to examine the effects of long-term aerobic and resistance exercise on health related fitness and physical activity in twenty adults with MS. Design. A repeated measures within subjects design was used. The adults exercised for 75 minutes, two times per week for twenty weeks. The adults performed 15 minutes of aerobic exercise (treadmill, recumbent bicycle, elliptical machines) at the beginning and at the end of each exercise session. In between, participants completed two-three sets of 6-15 repetitions of resistance training exercises designed to strengthen the whole body. The resistance training intensity was adjusted every three weeks based on the Kraemer et al., (2002) progression model. Participants were asked to record the number of steps taken per day for the first week of each month using a Walk-4-Life pedometer. The average number of steps taken over five days was compared between months. Cardiovascular endurance was assessed using the six minute walk. Muscular strength was defined as the peak torque of the knee flexors and extensors at 60° per second. Muscular endurance was defined as the total work performed during 30 repetitions at 180° per second. A repeated measures analysis of variance was used to examine changes in outcome variables between baseline, week 10 and week 20. Results. Eight participants dropped out of the study due to time constraints. After 20 weeks of exercise, 12 females (47 ± 8 yrs) had completed sixty-four percent of the 38 exercise sessions. Number of yards walked in six minutes, percent fat and the muscular endurance of the knee extensors did not significantly change during the intervention. However, there was a significant improvement of the endurance of the knee flexors between baseline and week 10 (F:(1,11) = 5.79 p = .035, ES = 0.35). Also, there was a significant improvement in the muscular strength of the knee flexors (F:(1,11) = 12.764, p = .004, ES = 0.54) and extensors (F:(1,11) = 6.47, p = .027, ES = 0.37) between week 10 and week 20. Monthly levels of physical activity significantly improved between months three and four. Conclusion. The combination of aerobic and resistance exercise was well tolerated, and was found to improve the muscular strength of the knee flexors and extensors in 12 females with MS.Keyword(s): adapted physical activity, exercise/fitness/physical activity, research