The pure rotational spectrum of calcium monomethyl, CaCH3 ((X) over tilde (2)A(1)), was recorded using the pump/probe microwave-optical double resonance (PPMODR) technique. The determined Fermi contact and dipolar parameters are: a(F) = -1.965(11) and T-aa = 2.180(18) MHz. The spin-rotation parameters are: epsilon(aa) = 6.702(49) and (epsilon(bb) + epsilon(cc))/2 = 555.5730(27) MHz. The mm-wave data [M. A. Anderson and L. M. Ziurys, Astrophys. J. 460, L77 (1996)] were reanalyzed to produce a set of fine structure parameters that are consistent with the PPMODR values and for which the standard deviation of the mm-wave data set is greatly reduced. A global fit of the two sets of data was performed to give an improved set of fine and hyperfine parameters for the (X) over tilde (2)A(1) state. The negative value for a(F) is inconsistent with a simple sigma-bond spin polarization model. A comparison among calcium containing molecules is made using hyperfine and spin-rotation parameters.