Consider the integrodifferential equation \[ \begin{multlined} y''(t) + \int^ t_ 0 k(t-s)y(s)ds+ \varphi(t) \int^ t_ 0 K(t-s)y'(s)ds =\\=f(t,y(t),y'(t),\int^ t_ 0 g(t,s,y(s),y'(s))ds), t \geq 0,\end{multlined}\tag{1} \] and \[ \begin{multlined} y''(t) + \int^ t_ 1 k({t\over s})y(s){1\over s}ds + \varphi(t) \int^ t_ 1 K({t\over s})y'(s)ds =\\= f(t,y(t),y'(t),\int^ t_ 1 g(t,s,y(s),y'(s))ds), t \geq 1.\end{multlined}\tag{2} \] The author proves, under some suitable conditions on the functions \(k\), \(K\), \(f\) and \(g\), that every solution of these equations has the form \(y(t) = A(t)\sin(\omega t + \delta(t))\) where \(\lim A(t)\), \(\lim\delta(t)\) exist as \(t\to \infty\). From this asymptote, the oscillatory behavior of the equations, the limit of the amplitudes, and the limit of the distance between consecutive zeros of the solutions are evident. Their definite values are also determined.