Einstein A-coefficients for transitions among the 3s23p3 states of S II, calculated with the CIV3 code, are found to be up to ∼25% different from those of Mendoza and Zeippen. These new results are used to derive the theoretical emission line ratio R = I(3s23p34s3/20–3s23p3 2D5/20)/I(3s23p34s3/20) = I(6717Å)/I(6730Å), which is a very useful electron density diagnostic for gaseous nebulae. The present diagnostics are up to ∼10% larger than those deduced using the A-values of Mendoza and Zeippen, and will lead to electron density estimates up to ∼50% greater.