Improved wood production is a major aim for walnut forests and especially for hybrid walnut (Juglans nigra x Juglans regia). This paper presents the first report describing the structure and function of a CDKA gene potentially involved in radial growth and wood production in walnut. We report the isolation of the full sequence of a CDKA gene by the use of degenerate primers and RACE approaches. We also describe the expression of the CDKA gene during radial growth. The analysis of intron sizes and positions as well as Southern-blot analysis suggest the presence of multiple copies (more than 2) of the CDKA gene in the hybrid walnut genome. Two different promoter sequences were cloned by the use of two different second-intron-specific primers.