AbstractNanocrystalline diamond (NCD) films were deposited on microscopic glass slides using the MW PECVD method (20 Torr, 710 °C, 0.8–1% CH4). After the growth period, the films were oxidized and subsequently hydrogenated, and some of them were doped with boron (NCD‐B; 3,000–30,000 ppm B:C; leading to ρ ∼ 10–1 Ω cm for the highest doped films). The neutron depth profiling showed that in the near surface region (<800 nm) the boron (10B + 11B) content in the highest doped sample was about (1.9 ± 0.3) × 1021 B cm–3 (i.e., 1.1 ± 0.2 at% of B). The films were seeded with human osteoblast‐like MG 63 cells (∼17,000 cells/cm2). On day 3 after seeding, the cell number on NCD (56,280 ± 1,090 cells/cm2) was significantly higher than that on NCD‐B (by 27 ± 3%), glass slides (by 22 ± 3%) and polystyrene wells (by 36 ± 3%). On day 7, the cell numbers on both NCD and NCD‐B films (351,170 ± 16,530 cells/cm2 and 310,020 ± 10,410 cells/cm2, respectively) became significantly higher than the values on glass slides and polystyrene dishes (218,800 ± 12,340 cells/cm2 and 223,400 ± 9,290 cells/cm2, respectively). Immunofluorescence staining showed that the cells on both NCD films assembled fine streak‐ or dot‐like focal adhesion plaques containing alphav integrins or talin, and a mesh‐like beta‐actin cytoskeleton. The cells on NCD‐B were brightly stained for osteocalcin, an important marker of osteogenic differentiation. Thus, both tested nanocrystalline diamond films gave good support for the adhesion, growth and maturation of bone‐derived cells. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)