This study assesses the prevalence of combined reading and arithmetic disabilities in 799 Dutch schoolchildren using standardized school achievement tests. Scores of arithmetic, word recognition, reading comprehension, and spelling of children in fourth and fifth grade were used. The main interest involved the co-occurrence of word recognition and arithmetic disabilities because of their possible relationship. The authors find a percentage of 7.6 for combined reading and arithmetic disabilities. Reading disabilities and arithmetic disabilities co-occurred more often than expected based on rates of the separate conditions. Children with combined reading and arithmetic disabilities seem to have more generalized achievement difficulties than single-deficit groups. Different operationalizations for reading disabilities (spelling and reading comprehension measures instead of word recognition) led, in part, to selection of other children. This might imply that different processes underlie the relationship between arithmetic and word recognition disabilities compared to the relationship of arithmetic disabilities with difficulties in spelling and reading comprehension. (Contains 5 tables.)