A facile procedure to direct the formation of hydroxyapatite (HAP) in preference to all other calcium phosphate phases and control over nanoparticle size distribution and morphology, with potential application in biomedical implants, is reported. The synthesis is performed in the presence of amine terminated diaminobutane poly(propylene imine) dendrimer (DAB). Aqueous solutions of calcium, phosphate, and DAB were used at different calcium: DAB molar ratios, viz. 2:1, 1:1, and 1:2 and the resulting suspensions were either kept at room temperature or hydrothermally treated at 80 degrees C for 16 h, or at 130 degrees C for 6 h. The resulting nanomaterials were fully characterized in terms of their physicochemical properties by means of XRD, TEM, SEM, and FTIR. It was found that DAB affects nucleation and crystal growth, as, in all cases, nanorods of hexagonal HAP with homogeneous and narrow size distributions (with mean sizes ranging from 10 nm x 5 nm up to 81 nm x 22 nm depending on synthesis conditions) were obtained.