Recently, it has been shown that statins increased cancellous bone formation and volume in 3-month-old rats and induced a minor decrease in osteoclast number. In the present study, one-year-old female rats were given simvastatin (10 mg/kg) or placebo daily for 3 months by a gastric tube. Specimens, 2.0 mm high, were cut transversely from the 5th lumbar vertebral body. The cancellous bone core diameters within the cortical shell of each specimen were delineated by a micro-CT scanner and then the cancellous bone was compressed in a materials testing machine between an upper and a lower platen with a diameter corresponding to the diameter of the cancellous bone core of each specimen. The cancellous bone volume was determined histomorphometrically on transverse sections. The cancellous bone volume in the simvastatin group (52.7 +/- 1.6%, mean value +/- SEM) was increased by 23% compared with the placebo group (42.8 +/- 1.7%). The compressive stress of the cancellous bone from the simvastatin group (31.8 +/- 2.7 MPa) was increased by 24% compared with the placebo group (24.1 +/- 1.9 MPa). No changes were found in cortical bone mass and strength after the statin treatment. In conclusion, statin given perorally to adult rats increased cancellous bone mass and increased cancellous bone compressive strength. The cancellous bone was found to possess normal biomechanical competence after the statin treatment.