Abstract: Using the ionospheric characteristic parameter f₀F₂ observed in more than 40 ionosonde stations distributed over the world, the response of the ionosphere to the geomagnetic storm event during May 1998 is studied by calculating the percentage deviation of the daily f₀F₂ value from its monthly median value for these stations which are divided into 5 regions according to their longitudinal distribution. The results showed that the characteristics of the ionospheric disturbance during the active phase of the storm can be explained by the storm circulation theory, but it seems that the positive disturbance appearing in the European region during the late recovery phase could not be attributed to this explanation.