This study was conducted to investigate the incidence of lameness in a private dairy herd and the effect of lameness on the weekly milk yields and lactation milk yield of dairy cows. Data used in the analyses comprised 953 lactation data from 787 Holstein cows. The traits analysed were daily averages of weekly milk yield and lactation milk yield. To determine the effect of lameness on daily averages of weekly milk yield, mixed model procedure was applied in the analyses. Lameness incidence of the herd was 9.02% and most of the lameness events were in the first four weeks. Daily averages of weekly milk yield had significantly decreased in the diagnosis week and continued at a reduced level until 3 weeks after the diagnosis. Whereas milk yield of healthy cows was 30.57 kg/d, milk yield in the lameness week, first week, second week and third week were 27.52 kg/d, 27.83 kg/d, 29.15 kg/d and 29.80 kg/d, respectively. Lame cows produced more milk while they were not lame and after the treatment, compared with healthy cows. The effect of lameness on lactation milk yield was not significant.