The effect of Temperature Humidity Index (THI) on dairy cows’ willingness to be on pasture was examined. Information for 2 years regarding weather, milk production, and time for voluntarily passing a gate between the barn and pasture of cows milked with an automatic milking system was studied. When the THI exceeded 72 during the day, more cows spent time on pasture compared to when the THI was less than 72 (27.0% vs. 19.2% of cows on pasture, respectively). However, the time of day influenced the proportion of cows on pasture, and when the THI exceeded 72, more cows were on pasture at night and less during the afternoon compared to days when the THI was less than 72. In conclusion, even under Swedish conditions, THI might have an effect on cows’ behaviour. However, when the cows have free access to roughage and pasture, an increased THI does not affect milk production.