Adiabatic potential energy surfaces (PES) of isomeric decalin cations have been found to be the pseudorotational surfaces due to avoided crossing that is typical for the highly symmetric Jahn-Teller active ions rather than for low-symmetric bicyclic systems. According to the UB3LYP/6-31G* data, the height of the barrier to pseudorotation is less than 2 kcal/mol for the trans isomer and about 9 kcal/rnol for the cis isomer. Another peculiarity of the cis isomer PES is that the structure of minimum energy lies beyond the pseudorotation clutter. The calculation results are in fair agreement with the experimental electron spin resonance data.