Abstract Excessive drill string vibration can lead to partial or catastrophic failure of bottom hole assembly (BHA) components. This paper presents data from a microprocessor based downhole vibration data acquisition and recording system, located within a host MWD (Measurement While Drilling) collar in the BHA. Four case studies of vibration levels attained during commercial drilling operations are presented. These examples include vibration monitoring during reaming, drilling a casing shoe, and drilling new formation. Generally, lateral accelerations were an order of magnitude greater than longitudinal accelerations. In one example, catastrophic failure of MWD components resulted from sustained high-level lateral vibrations. Data collected to-date has been used to optimize BHA components and define the down hole vibrational environment. Future information obtained by the monitoring system will be of value in verifying and calibrating computer models.