Well-crystallized, compositionally homogeneous HA whiskers with uniform morphology and high aspect ratio were successfully prepared by hydrothermal homogeneous precipitation from aqueous solution using acetamide (AA). The product had a mean length of 116 mu m and an aspect ratio of 102. The nucleation and crystal growth of such whiskers were studied by quenching the solution from various temperatures. It was found that the nuclei could be formed at about 120 degrees C, while stable and well-grown whisker-like precipitation only occurred above 140 degrees C. The product had the same crystallographic characteristics as normal HA crystals. No other phase than HA was detected. Compared with widely used wet chemical routes, the slow hydrolysis of AA provided a stable and continuous growth environment with a low degree of supersaturation, facilitating rapid growth of long HA whiskers directly from a hydrothermal solution, free of any interference from other phases. The whiskers showed spiral growth, with preferential c-axis orientation.