The objective of the study was to compare Bacillus subtilis spore film dosimeters with a Robertson Berger UV meter (RB meter) and diary records for assessing personal UV-B doses during a 13-day heliotherapy (HT) for atopic dermatitis (AD). In addition, the relationship between the personal UV-B dose and change in serum 25-hydroxyvitamin D (25(OH)D) was studied. Altogether 21 adult patients with AD completed the study arranged in the Canary Islands, either in January or March 2005. The spore film dosimeters were used throughout the day during the HT. Serum 25(OH)D was analyzed using radioimmunoassay. The mean personal UV-B dose measured with the dosimeters was 75 SED in January and 131 SED in March. The respective results gained from the RB meter combined with diary records were 63 SED and 119 SED showing a close correlation with the dosimeter results. Serum 25(OH)D concentration increased by 9.7 nmol L−1 in January and by 26.0 7 nmol L−1 in March. The increase in serum 25(OH)D correlated with the UV-B dose received. The patients complied well to use the dosimeters. We conclude spore films to be a feasible and reliable personal UV dosimeter in vivo in field conditions.