A coincidence degree theorem due to Mawhin is applied to show the existence of a solution to the multipoint boundary value problem for the nonlinear second-order equation \[ u''=f(t,u,u') , \qquad t \in (0,1)\,, \] \[ u'(0)= u'(\eta)\,, \qquad u(1)=\sum^{n}_{i=1}\alpha_{i} u(\eta_{i})\,, \] where \(\,0< \eta \leq 1,\, \sum^{n}_{i=1}\alpha_{i}=\sum^{n}_{i=1}\alpha_{i} \eta_{i} =1\, \) and \(f\) satisfies the Caratheodory conditions. Sufficient conditions are given in order to prove the existence of at least one solution. Both boundary conditions are responsible for resonance.