Daily life of the individual is characterized by a rhythm determined by the circadian system. Circadian rhythms are cycles which run around 24 h and are associated with widespread physiological and psychological effects. The relative influence of genetic and environmental factors on circadian rhythms and their effect on associated variables is not well understood yet. We performed a pilot study in 21 pairs of female twins (12 monozygotic [MZ] and 9 dizygotic [DZ]), with a BMI 24.3 ± 2.8 and mean age 48 ± 2. The sample was selected from the participants in the Murcia Twin Register. Circadian patterns were studied by analyzing wrist temperature and actimetry, measured continuously during 1 week. Preliminary results show a consistent pattern of higher intra-pair correlations between MZ twins. This pattern points to moderate to high heritability for most of the variables analyzed, suggesting a relevant genetic influence in the chronobiology of the studied women.