Introduction Although resistance type exercise training (RT) effectively increases muscle mass and strength in older individuals, it remains unclear whether gains in muscle mass and strength are maintained without continued supervised training. We assessed the capacity of older individuals to maintain muscle mass and strength gains one year after partaking in a successful RT program. Methods Fifty-three healthy older adults performed a 24-wk supervised RT program. Upon the cessation of the training program, participants were not provided with any advice or incentives to continue exercise training. One year after completion of the training program, all participants were contacted and invited back to the laboratory to assess anthropometrics, body composition (DXA), quadriceps muscle cross-sectional area (CSA) (CT-scan), muscle strength (1RM knee extension/leg press), and muscle fiber characteristics (muscle biopsy). Following primary analyses on all participants that responded to the invitation (n = 35), participants were divided into two groups: individuals who had continued to perform exercise training on an individual basis (EXER group; n = 16) and individuals who had not continued to perform any regular exercise (STOP group; n = 19) after completing the RT program. Results The initial increases in quadriceps CSA (+506 ± 209 and +584 ± 287 mm2) and knee extension strength (+32 ± 12 vs +34 ± 10 kg) after the 24-wk RT program did not differ between the STOP and EXER group (all P > 0.05). One year after discontinuation of the RT program, participants had lost muscle mass (P < 0.01), with a greater decline in quadriceps CSA in the STOP vs EXER group (−579 ± 268 vs −309 ± 253 mm2, respectively; P < 0.05). Muscle strength had decreased significantly compared to values after completing the RT program (P < 0.01), with no differences observed between the STOP vs EXER group (knee extension: −21 ± 8 vs −18 ± 8 kg, respectively; P > 0.05), yet remained higher compared with values before the RT program (P < 0.05). Conclusion Though prolonged RT can effectively increase muscle mass and strength in the older population, muscle mass gains are lost and muscle strength gains are only partly preserved within one year if the supervised exercise program is not continued.