DNA-dependent DNA synthesis in vitro by human immunodeficiency virus-1 reverse transcriptase is relatively error-prone. The enzyme, whether recombinant or from virus particles, produces errors while replicating M13mp2 DNA at a rate that, if operative in vivo, would produce about five mutations per genome per round of replication. Sequence analysis of mutants resulting from in vitro synthesis demonstrates that errors are nonrandomly distributed. Base substitution and one-base frameshift mutational hot spots are observed. The specificity and position of errors suggest that most of the frameshifts and many of the base substitutions are initiated by template-primer slippage. Processivity analysis for the enzyme on the M13mp2 DNA template reveals strong termination at specific sites. Termination sites within homopolymer sequences correlate with frameshift mutational hot spots. The results suggest that the formation and/or utilization of misaligned template-primers is increased during the dissociation-reinitiation phase of the reaction.