  By using Riemann--Hilbert problem based techniques, we obtain the asymptotic
expansion of lacunary Toeplitz determinants $\det_N\big[ c_{\ell_a-m_b}[f]
\big]$ generated by holomorhpic symbols, where $\ell_a=a$ (resp. $m_b=b$)
except for a finite subset of indices $a=h_1,\dots, h_n$ (resp. $b=t_1,\dots,
t_r$). In addition to the usual Szeg\"{o} asymptotics, our answer involves a
determinant of size $n+r$.
