We report on the influence of observer presence and handling on activity patterns (stride frequency) of the Australian sleepy lizard (Tiliqua rugosa). Over a 17–week period, we maintained continuous records of activity of 10 adult lizards using lightweight activity loggers recording lizard body temperature and stride frequency every two minutes. At all times of day and throughout the season, we recorded the effect of three levels of observer disturbance (observed only, briefly handled [< 60 sec], and held for an extended period [30–45 min]), on lizards either inactive or active at the time of interaction. Following all disturbance types, there was an increase in average stride frequency that lasted for up to an hour. This is a significant period for an animal that is generally active for only a few hours in the day. The extent of this effect was higher for active than for inactive lizards, when observed or briefly handled, and increased with the level and duration of the disturbance. Both inactive and active lizards when held for an extended period responded with a very high average level of activity. We found that shifts to behavior following brief handling (e.g., attaching a cotton spool) can be minimized or prevented by working with inactive lizards early in the morning, when ambient temperatures (and hence lizard body temperatures) are relatively low. Protocol design for field-based behavioral studies involving lizards must avoid, or if necessary compensate, for biases that result from the effect of different levels of observer disturbance on activity patterns.