The excitation spectrum of 1,6-epoxy-[10]annulene in the region of the lowest electronic transition (approximate to 417-390 nm) has been measured under supersonic expansion conditions. The observed vibronic structure, with onset at 24 008 cm(-1), is discussed mostly in terms of allowed transitions. Comparison with MCSCF/CAS calculations of vibrational frequencies in S-0 and S-1 allows the assignment of several excited state fundamentals and correlation with ground state modes. Both the experimental and theoretical results point to the conclusion that equilibrium geometry changes upon excitation, with the C-1 and C-6 atoms of the molecular ring, connected by the epoxy bridge, moving slightly apart going from S-0 to S-1.