Carbon nanofibers have exceptional theoretical mechanical properties (such as low weight to strength ratios) that, along with possessing nanoscale fiber dimensions similar to crystalline hydroxyapatite found in bone, suggest strong possibilities for use as an orthopedic/dental implant material. To determine, for the first time, cytocompatibility properties pertinent for bone prosthetic applications, osteoblast (bone-forming cells) and fibroblast (cells contributing to callus formation and fibrous encapsulation events that result in implant loosening) adhesion were determined on carbon nanofibers in the present in vitro study. Results provided evidence that, compared to conventional carbon fibers, nanometer dimension carbon fibers promoted select osteoblast adhesion. To determine properties that selectively enhanced osteoblast adhesion, similar cell adhesion assays were performed on polymeric (specifically, poly-lactic-co-glycolic; PLGA) casts of carbon fiber compacts previously tested. Compared to PLGA casts of conventional carbon fibers, results provided the first evidence of enhanced select osteoblast adhesion on PLGA casts of nanophase carbon fibers. The summation of these results demonstrate that due to a high degree of nanometer surface roughness, carbon fibers with nanometer dimensions may be optimal materials to selectively increase osteoblast adhesion necessary for successful bone implant applications.