To evaluate the effects of the 1993 flood in the upper Mississippi River Basin on the determination of flood magnitude and frequency, discharges that had recurrence intervals of 10, 25, 50, and 100 years computed from data through the 1992 water year were compared with those computed from data through the 1993 water year for 62 selected streamflow-gaging stations in Iowa. On the basis of the flood-frequency analysis computed from data through the 1993 water year, a flood that was greater than or equal to a 10-year recurrence-interval discharge occurred during 1993 at all 62 gaging stations, and a flood greater than or equal to a 100-year recurrence-interval discharge occurred at 11 of the gaging stations.