I find that son preference is persistently strong in Hong Kong. Firstborn girls increased fertility as well as the probability of boys in the future. Compared with firstborn boys, firstborn girls caused mothers to have on average 6.74% more children in the 1991 to 2016 censuses, and the magnitude of the effect decreased with time. Concurrent with the diminishing effect of firstborn girls on fertility, son-biased sex selection might became more extensive. In the most recent data from the 2016 census, parents without sons were 20% more likely to have sons at the third parity than parents who already had at least one son. The results suggest that son preference is persistently strong in Hong Kong, and parents might be increasingly likely to substitute the son-biased stopping rule with sex selection to have sons such that they could reach the desired number of sons within the small family.