Based on near-surface temperature measurements conducted at high temporal resolution in 16 Scottish lochs in 2001, a strong seasonal cycle was observed in the magnitude of the diel surface temperature range (DSTR). The influence of 5 site-specific potential predictor variables including altitude, latitude, longitude, lake surface area, and maximum lake depth on the timing of the start and end of a statistically significant DSTR was investigated. The DSTR is important because it is expected to have implications for many processes that affect biogeochemical cycling in lakes, including the rates of metabolic processes. The timing of the start of a statistically significant DSTR in spring showed a strong dependence on altitude, a much weaker dependence on latitude, but no dependence on any other predictor variable tested. The timing of the end of a statistically significant DSTR in autumn showed no dependence on any of the predictor variables tested. Because the start of a statistically significant DSTR is dependent on altitude but its end is not, its duration is also dependent on altitude. Because the start of a significant DSTR is related to the onset of thermal stratification, the results suggest that the altitude of a lake will affect the timing of the onset of thermal stratification and its duration.