Adults' simple arithmetic performance is more efficient when operands are presented in Arabic digit (3 + 5) than in number word (three + five) formats. An explanation provided is that visual familiarity with digits is higher respect to number words. However, most studies have been limited to single-digit addition and multiplication problems. In this article, we examine to what extent format effects can be found in the context of arithmetic word problems, in which visual familiarity is reduced (Manuel had 3 marbles, and then Pedro gave to him 5). Participants with high and low arithmetic fluency solved addition and subtraction word problems in which operands were presented in both formats. The overall results showed an advantage for digits operands relative to words operands. In addition, the format effects were more evident for subtraction and low-skilled participants. These results were interpreted in terms of more rapid access of digits to numerical magnitude.