Mastitis is a significant disease in cattle breeding. Mastitis is divided into clinical and subclinical mastitis. Typical symptoms of clinical mastitis are swelling redness, soreness of the mammary gland, flakes in the milk, or milk-not-like secretion. The phenotypic relationships among udder conformation traits, the incidence of clinical mastitis, and somatic cells were analyzed in Czech Holstein cattle. The clinical mastitis was considered an all-or-one trait with 0 (no clinical mastitis case) and 1 (at least one clinical mastitis case). The incidence of clinical mastitis was monitored in seven lactation periods of 50 days and for the whole lactation. The somatic cell count was transformed into a somatic cell score for normal data distribution. Somatic cell score was monitored in 10 periods after 30 days and, on average, for the whole lactation (logarithmic recalculation of the arithmetic mean somatic cell count). The total number of cows was 17,622. All records were related to the first lactations. The phenotypic correlation of observed data for the characteristics ranged from -0.13 to 0.69. These correlations were referred to as phenotypic. The relationships were evaluated by linear and logistic animal model. There were proposed appropriate selection criteria for the selection of heifers. It was solid and tight forequarters, the position of the front and rear teats inside of quarter, intermediate teat length, shallow udders, high rear udder height, deep ligament, udder width 10 – 12 cm and a body condition score of 2.5 – 4. The optimal score of the conformation traits considering low incidence of clinical mastitis mostly coincided with the optimal score of low somatic cell score.