A popular but unsubstantiated belief is that a reading disability is the most prevalent type of learning disability (LD), that LD in mathematics is rare, and that LD in written expression is very rare. In 485 clinical children administered the WISC-III and WIAT, 65 percent had LD. The most common was LD in written expression (92 percent), either alone (50 percent) or in combination with LD in reading and/or mathematics (42 percent). Only 4 percent of the children had LD in reading alone, and 4 percent had LD in mathematics alone. Total LD percentages for reading and mathematics were similar (33 percent and 32 percent). Children with writing problems had far greater difficulty with compositional skills than with spelling. (Contains 3 tables and 1 note.)