Robotic milking systems (RMS) are becoming more common in the USA, but there is yet limited research available. The objective of this study was to compare daily milk production, number of milkings, robot box feed consumption and rumination time between primiparous and multiparous (2nd and > parity) cows in RMS at various stages of lactation. Data were collected daily from 31 farms for approximately 18 mo and analyzed up to 400 DIM. Eight categories of DIM were evaluated: < 7, 8–30, 31–60, 61–90, 91–120, 121–150, 151–250, and >250 DIM (but only some are reported). A mixed model analysis was conducted with parity, DIM category and parity × DIM category included as fixed effects and farm as random effect. Daily milk production (n = 2,703,075 cow-d) differed between primiparous and multiparous cows at all stages of lactation with a parity*DIM detected (P < 0.001). Notably milk production (primiparous and multiparous, respectively) was 15.6 and 24.2 kg for <7 DIM; 30.2 and 43.2 kg for 31–60 DIM (when multiparous cows peaked); 31.3 and 42.4 kg for 61–90 DIM (when primiparous cows peaked); and 25.2 and 24.3 kg for >250 DIM. Number of milkings/d (n = 2,703,075 cow-d) followed a similar pattern and also differed between parities with a parity × DIM detected (P < 0.001). Milkings/d was 1.87 and 2.50 for <7 DIM; 2.58 and 2.99 for 31–60 DIM, 2.64 and 2.96 for 61–90 DIM, and 2.39 and 2.23 for >250 DIM, for primiparous and multiparous cows, respectively. In addition, daily robot pellet consumption (n = 2,697,998 cow-d) also differed between parities with a parity × DIM detected (P < 0.001). Consumption was 2.93 and 3.29 kg for <7 DIM; 5.37 and 6.49 kg for 31–60 DIM and was reduced to 3.76 and 3.74 kg for >250 DIM for primiparous and multiparous cows, respectively. Consumption peaked at 31–60 DIM for both parity categories. Daily rumination (n = 1,465,606 cow-d) averaged 422.1 and 465.3 min for primiparous and multiparous cows (P < 0.001), respectively. It appeared that primiparous cows in RMS produced less milk in comparison to multiparous cows than expected (estimated peak milk ratio of 0.72) which suggests that performance benefits may be achieved by improving management of these cows in RMS.