The aim of the present study was to investigate the performance in arithmetic related to achievement levels in reading and mathematics. Basic arithmetical facts and multi-step calculations were examined. The participants were 941 pupils aged 8 (N = 415), 10 (N = 274) and 13 (N = 252) years. The pupils were divided into four groups by standardized achievement tests. One group showed low achievement in both mathematics and reading (MLRL), a second group showed low achievement in mathematics only (ML-only), a third group in reading only (RL-only) and a fourth group showed normal achievement in both mathematics and reading (NA). The ML-only and the MLRL groups did not differ significantly in basic arithmetical facts at any age level, but both groups performed below the RL-only and NA groups. The two latter groups also performed similarly at all year levels. In multi-step calculation all groups differed significantly at the lowest age level, with the NA as the group with the best achievement, followed by RL-only, ML-only and the MLRL group. At the two highest age levels the relations between the groups, in multi-step calculation, were in accordance with the results regarding basic facts. The findings indicate, for both normal and low general mathematical ability, that low achievement in reading to a small extent interferes with the pupils development of arithmetic performance. (Contains 3 tables.)