The CM class number one problem for elliptic curves asked to find all elliptic curves defined over the rationals with non-trivial endomorphism ring. For genus-2 curves it is the problem of determining all CM curves of genus 2 defined over the reflex field. We solve the problem by showing that the list given in Bouyer–Streng [3, Tables 1a, 1b, 2b, and 2c] is complete.