AbstractFor systems above the marginal dimensiond*, where mean field theory starts to become valid, such as Ising models ind= 5 for whichd* = 4, hyperscaling is invalid and hence it was suggested that finite size scaling is not ruled by the correlation length ξ (∝ |t|−1/2in Landau theory,tbeing the distance from the critical point) but by a “thermodynamic length”l(∝ |t|−2/d). Early simulation work by Binder et al. using nearest neighbor hypercubicL5lattices withL⩽ 7 yielded some evidence for this prediction, but the renormalized coupling constantgL= −3 + 〈M4〉/〈M2〉2atTcwasgL≈ −1.0 instead of the prediction of Brézin and Zinn‐Justin,gL(Tc) = −3 + Γ4(1/4)/(8 π2) ≈ −0.812. In the present work, we try to shed light on this controversy obtaining much more precise Monte Carlo data using multihistogram techniques and lattices as large asL= 17 (i.e., 1419857 Ising spins). While our value ofTcagrees nicely with recent high temperature series work (KBTc/J≈ 8.7774 ± 0.0035), the coupling atTc{gL(Tc) ≈ −0.958 ± 0.050} confirms the work for small lattices and disagrees with the analytical prediction. Hence the data are better consistent with a shift of the effective critical temperatureTc(L) ‐Tc(∝) ∝L−d/2 rather than withL−(d−2)according to the analytical theory. If the latter behavior is cor