This study focused on analyzing children's difficulties with two-step mathematical word problems. Seventy-one fifth-grade children in Puerto Rico were individually observed solving five problems. Two of these were two-step problems; the remaining three were one-step problems with the same mathematical structures as the components of the two-step problems. Performance was significantly poorer on the two-step problems than on the one-step problems. Forty-eight (66.6%) children had difficulties with the two-step problems. The difficulties stemmed from different sources: lack of understanding of the concepts and relationships involved in the problem; incorrect strategy for working any word problem; using a single operation to solve two-step problems; and difficulties with a mismatch between order of presentation and order of operation. The implications for education of these results are briefly discussed. (Author/MNS)