Bovine mastitis is a common and complex infectious disease that has an impact on the milkmaid production of the Ayacucho region. With the aim to determine the frequency of subclinical mastitis and to associate some factors: age, number of births and lactation period. A total of 95 Brown Swiss cattle were evaluated in milk production at the Allpachaca farm of the National University of San Cristobal de Huamanga (UNSCH), Ayacucho, Peru; located at coordinates 13° 23'30.79"S; 74° 15'56.48"W, with an altitude of 3528 meters over sea level. To estimate the frequency of the disease, the PortaSCC® somatic cell count kit (CCS) and the California Mastitis Test (CMT) were used; and the Chi-square statistical test was used to determine dependence on the associated factors. 82.1% and 69.5% of frequency of subclinical mastitis by CMT and CCS, respectively were obtained, considering traces as positive for both tests; and 65.3% and 62.1% of frequency of subclinical mastitis considering the traces as negative. Of the three variables evaluated, two of them have an association relationship because it indicates that older cows and greater number of births are at greater risk for subclinical mastitis. According to the Cohen's Kappa Index statistical test, there is a good agreement between the CMT test and CCS.