The CRISPR-Cas9 system has been employed to generate mutant alleles in a range of different organisms. However, so far there have not been reports of use of this system for efficient correction of a genetic disease. Here we show that mice with a dominant mutation in Crygc gene that causes cataracts could be rescued by coinjection into zygotes of Cas9 mRNA and a single-guide RNA (sgRNA) targeting the mutant allele. Correction occurred via homology-directed repair (HDR) based on an exogenously supplied oligonucleotide or the endogenous WT allele, with only rare evidence of off-target modifications. The resulting mice were fertile and able to transmit the corrected allele to their progeny. Thus, our study provides proof of principle for use of the CRISPR-Cas9 system to correct genetic disease. Display omitted •A dominant cataract-causing mutation in the Crygc gene is corrected using CRISPR-Cas9•Genetic correction via HDR uses information from the endogenous WT allele•Genetic correction can also occur using information from an exogenous oligo•The rescued mice can transmit the corrected allele to their progeny The authors show genetic rescue of a dominant cataract-causing mutation in mice using an injection of CRISPR-Cas9 and a guide RNA into zygotes.