We carried out a comparative analysis of circadian rhythms of melatonin secretion in Caucasian menopausal women with and without insomnia depending on the 3111T/C polymorphism of the Clock gene. Melatonin levels was measured in the saliva 4 times a day (06.00-07.00, 12.00-13.00, 18.00-19.00, and 23.00-00.00 h). Carriers of the TT genotype with insomnia demonstrated significantly higher level of melatonin in the early morning hours compared to the carriers of the minor allele C (12.60±7.58 and 8.98±8.62 pg/ml, respectively, p=0.023). In the control group, no statistically significant differences were revealed. The carriers of the TT genotype with sleep disorders have higher morning melatonin level compared to control group women (12.60±7.58 and 5.48±4.74 pg/ml, respectively, p=0.005) and low nocturnal melatonin level (6.42±4.97 and 12.52±10.40 pg/ml, respectively, p=0.039).