This study assesses the prevalence of combined reading and arithmetic disabilities in 799 Dutch schoolchildren using st dardized school achievement tests. Scores of arithmetic, word recognition, reading comprehension, and spelling of child in fourth and fifth grade were used. The main interest involved the co-occurrence of word recognition and arithmetic d abilities because of their possible relationship. The authors find a percentage of 7.6 for combined reading and arithme disabilities. Reading disabilities and arithmetic disabilities co-occurred more often than expected based on rates of the s arate conditions. Children with combined reading and arithmetic disabilities seem to have more generalized achievem difficulties than single-deficit groups. Different operationalizations for reading disabilities (spelling and reading comp hension measures instead of word recognition) led, in part, to selection of other children. This might imply that differ processes underlie the relationship between arithmetic and word recognition disabilities compared to the relationship arithmetic disabilities with difficulties in spelling and reading comprehension. © 2008 Hammill Institute on Disabilities.