Midstratospheric trajectories for February and March 1979 are calculated using geopotential analyses derived from limb infrared monitor of the stratosphere (LIMS) data. These trajectories are compared with the corresponding results using stratospheric sounding unit (SSU) data. The trajectories are quasi isentropic in that a radiation scheme is used to imply cross-isentrope flow. The results show that in disturbed conditions, quantitative agreement between the trajectories, that is, within 25 great circle degrees (GCD) (one GCD ≈ 110 km) may be valid for only 3 or 4 days, whereas during quiescent periods, quantitative agreement may last up to 10 days. By comparing trajectories calculated with different data some insight can be gained as to errors due to vertical resolution and horizontal resolution (due to infrequent sampling) in the analyzed geopotential height fields. For the disturbed trajectories described in this paper the horizontal resolution of the data was more important than vertical resolution. For the quiescent trajectories described in this paper, which could be calculated accurately for a longer duration because of the absence of appreciable transients, the vertical resolution of the data was found to be more important than the horizontal resolution. It is speculated that these characteristics are also applicable to trajectories calculated during disturbed and quiescent periods in general. A review of some recently published trajectories shows that the qualitative conclusions of such works remains unaffected when the calculations are repeated using different data.