Although scorpions are common and potentially ecologically important members of arid ecosystems throughout the world, basic life history information is lacking for most species. In the current study I examined reproductive investment patterns in four species of scorpion (Centruroides exilicauda, Vaejovis spinigerus, Diplocentrus peloncillensis, and Pseudouroctonus apacheanus) from southeastern Arizona and southwestern New Mexico during 1996–1998. Vaejovis spinigerus invested more in reproduction, in both absolute (total litter mass, TLM) and relative (TLM divided by female mass) terms, than did the other species, and produced the largest litters. Offspring of D. peloncillensis were the largest, weighing over twice as much as the next largest juveniles. Female size was uncorrelated with offspring size in any species, but positive correlations were found between female size and both litter size and total litter mass for C. exilicauda (marginally significant) and V. spinigerus (after removal of an outlier). Greater reproductive investment, measured as TLM, was used to make more offspring (in all species but P. apacheanus) but not larger offspring. A marginally significant trade-off between offspring size and number was found in V. spinigerus; there was no size-number trade-off in the other three species. Overall, then, my results suggest that (1) larger females do not produce larger offspring, (2) larger females may produce more offspring and invest more into a reproductive bout, and (3) the allocation strategy of these species appears to be to invest reproductive resources into production of as many offspring as possible of a relatively fixed size.