The A(1)Sigma(+)-X(1)Sigma(+) electronic transition in CaS has been rotationally analyzed using high-resolution, laser excitation spectroscopy. Doppler-limited spectra were recorded for the 0-0, 1-0, 1-1, 2-1, 3-1, 3-2, 4-2, 4-3, 5-3, 5-4, 6-4 and 6-5 bands with a measurement precision of approximately 0.003 cm(-1). In total, more than 1200 line positions have been measured, assigned and employed in least-squares fits of molecular parameters. The A(1)Sigma(+) state is extensively perturbed and level crossings have been identified and analyzed in the A(1)Sigma(+) upsilon = 3; 4, 5, and 6 vibrational levels. The perturbations are believed to arise from interactions of the A(1)Sigma(+) state with the a(3)Piand A'(1)Pi states. Term values and effective rotational parameters for the perturbing, states are obtained through a partial deperturbation analysis of the perturbed bands. Estimated values of the principal molecular parameters are T-00 = 15194.428(2) cm(-1), R-e' = 2.38626(16) Angstrom, and omega(e)' = 409.077(9) cm(-1) for the A(1)Sigma(+) state, and R-e" = 2.31770(14) Angstrom and omega(e)' = 462.273(12) cm(-1) for the X(1)Sigma(+) state.