The Minnesota Study of Twins Reared Apart (MISTRA) was initiated in 1979 and continued until 2000. It consisted of 139 pairs of twins who had been separated in early childhood and not re-united until adulthood, and members of their families. As part of a broader assessment, these participants completed 42 mental ability tests from three well-known test batteries. In this article, we present some background on the sample and tests and the correlation matrix of test scores, for the use of other researchers. As in all science, however, replication across samples of both tests and participants remains key to the development of ideas about mental ability.