Crossbreeding has been considered as a quick way of increasing performance of low productive tropical breeds. Crossbreeding of indigenous cattle with exotic such as Holstein is underway in Pakistan for the last four decades. Data on first lactation milk yield of crossbred dairy cattle (n=2025) from three Military dairy herds for 1985-2006 were used for this study to evaluate performance of crossbred dairy cattle. The exotic cattle represented mainly Holstein while Jersey, Ayrshire and Red Dane were also used sporadically. The local cattle were generally Sahiwal. The total first lactation milk yield for crossbreds averaged 1633±47.0 kg. The highest total milk yield was found for Neelum Military dairy farm (2328±62.3 kg) and lowest for Lahore Military dairy farm (1356±50.1 kg). These values had almost 1000 kg range. The first lactation length in this study averaged 240±5.5 days. Cows had longest lactation length at NeelumMilitary farm (264±6.8 days) while cows at Lahore Military farm (229±5.5 days) had the shorter lactations. First lactation performance of different genetic groups showed higher total milk yield for 50% exotic inheritance (1749±33.3 kg) as compared to all other genetic groups. The lowest total milk yield was found for ≤25% exotic inheritance (1567±171.3 kg). The season of calving had non-significant effect on milk yield and lactation length while year of calving affected both traits significantly. Phenotypic trends revealed that first lactation milk yield and lactation length increased @ 27.7 kg/year and 0.45 days/year respectively, from 1985 to 2005. Managemental and feeding differences at various farms accounted for most of the variation in first lactation milk yield. The performance of these crossbreds as compared to buffaloes with average first lactation milk yield of 1800 kg or those of Sahiwal purebreds (1430 kg) challenges the sustainability of the system especially when demands of these crossbreds are higher to cope with disease and environmental stresses.