High quality Cu In S ₂ single crystals, grown by the traveling heater method in an indium solvent, were studied using reflectance and photoluminescence at 4.2 K . The first, E_A(n=2)=1.5494 eV , and second, E_A(n=3)=1.5532 eV , excited states of the A free exciton have been observed in the photoluminescence spectra. Accurate values of the A exciton binding energy E _FE ^A=18.5 meV and Bohr radius a_B^A=3.8 nm , bandgap E_g=1.5540 eV at 4.2 K and static dielectric constant ε=10.2 have been derived assuming a hydrogenic model.