Ubbelohde viscosity measurements were performed on dilute solutions of perfluorosulfonated ionomers (PFSI) in various solvents exhibiting quite different dielectric constants. With aliphatic alcohols as solvents an increase of the reduced viscosity with dilution is evident. This effect is analogous to the so-called ’polyelectrolyte effect’ observed for highly charged ionic polymers in polar solvents. The polyelectrolyte effect increases with the dielectric constant for alcohols, is similar in water and in methanol solutions, and disappears for high polarity solvents. This evolution is discussed in terms of an increase of the electrostatic persistence length. The viscosimetric behaviour of PFSI solutions is shown to fit well with the Liberti-Stivala equation.