This study assessed the effects of Nordic winter conditions on horses kept permanently outdoors, but provided with a sheltered area. The average incidence of being outdoors was 70 %, although the horses spent most of their time outdoors under all weather conditions. Temperatures went as low as -31 °C. The horses made more use of the shelter under low ambient temperatures. There was a strong tendency for increased shelter use in response to rain and wind, but snow had no effect on shelter usage. Shivering behaviour was observed only once on a single horse during a rainy day at +5 °C. In addition to behaviour, body condition score, coat length and serum thyroid hormone (T4) level were recorded. Neck coat length reached an average maximum of 4.6 ± 0.9 cm. Body condition score remained satisfactory over the winter months. There was no correlation between serum T4 and ambient temperature. Results of this study indicated that cold climates with temperatures as low as -31 °C do not challenge the thermoregulation of cold-acclimated Icelandic horses as long as there is sufficient quality feed and access to shelter.