The Machine Shop of Larsen & Toubro Limited has a CNC controlled, vertical spindle machining center for high accuracy machining. It is a dual spindle machine, which is presently used for deep-hole drilling operation. The gantry of this machine was reported to undergo lateral distortions (200-400 microns) at slave end with respect to time. For a special high precision job, machining with this distortions of the machine was not meeting the tight tolerance requirements. The reasons for these distortions were investigated and measurements were carried out. The effects of variation in environmental conditions on machine distortions were analyzed by finite element method using ANSYS 6.1 package. The trend of the analysis results closely matched with the actual measurements. This provided the clues in providing the proper solution. After implementation of the solution experiments were carried out to check the effectiveness of the solution. The measurements indicated that the distortions were controlled and requirement of machining accuracy established.