A neglected consequence of declining fertility is the likely rise of families with children of one sex-only sons or only daughters. Increases in such families present important demographic shifts that may weaken patrilineal family systems. We assess whether sons-only and daughters-only families rose in Asia and North Africa from the early 1990s to around 2015. Using 88 surveys and two censuses, we examine how the number and sex composition of children of mothers aged 40-49 changed across 20 countries, representing 87% of the region's population and 54% of the global population. We also compare observed trends to sex-indifferent counterfactuals, quantify contributions of fertility declines with decompositions, and investigate subnational trends in China and India. Increases in sons-only families were universal where numbers of children fell. Growth of daughters-only families was suppressed in patrilineal contexts, but these sonless families still rose significantly in 13 of 18 countries where numbers declined. By 2015, over a quarter of families in the region had only sons and nearly a fifth only daughters. There was considerable variation across countries: recent levels ranged from 28.3% to 3.4% daughters-only and from 40.1% to 6.0% sons-only. China and the rest of East Asia had the highest shares.