The objective of this study was to describe daily body weight (BW) changes in the first 100 days of lactation in confined dairy cows and to associate BW loss with productive and reproductive performance. Data included 26,344 daily BW measurements of 372 Holsteins calving between June 2011 and June 2012 in a commercial herd in the South of Brazil. Cows were automatically weighed and were assigned according to parity. Individual measurements were smoothed using cubic splines, generating nadir BW, days to nadir BW and the BW loss (absolute and relative values). This approach used days in milk (DIM) as a single smoothing variable. Body weight at calving differed across parities: 570.5, 653.5, and 699.9 kg, for the 1st, 2nd and 3rd and subsequent parities, respectively. Body weight at nadir also differed across parities: 521.5, 608.8, and 647.3 kg, respectively. Mean days from calving BW to nadir BW and mean loss of BW (kg) from calving to nadir BW did not differ across parities, but relative BW change (kg/100 kg) was larger in animals in first parity (-8.4 kg/100 kg) than second parity (-6.6 kg/100 kg). However, cows in first parity had more chances for good reproduction than cows in third and subsequent parities (44.0% vs. 30.7%, respectively). There was no difference in the probability of adequate reproduction (pregnant until 180 DIM) among cows with low, medium, or high milk yield. Furthermore, cows with low and medium BW loss (below 60 kg of BW change) showed more likelihood to adequate reproduction than cows with high BW loss (above 60 kg of BW): 45.5 and 45.8% vs. 24.4%, respectively. Improvements in fertility of dairy cows should be achieved by minimizing body weight loss in early lactation.