Treatment of mastitis may be improved by earlier detection through use of sickness behaviors. The objective was to determine the relationship between clinical signs of mastitis, induced by a Streptococcus uberis challenge, and resting behavior of early lactation dairy cows. Holstein cows in their second (n = 21) and third (n = 7) lactation were enrolled and intramammary challenges were conducted with S. uberis (10,560 ± 1,855 cfu) within 1.2 ± 0.7 d after calving. Somatic cell count, milk score (MS), and udder inflammation score (US) were collected 24 h and 0 h before challenge, every 12 h for 3 d post-challenge, and daily on d 4–7. MS and US were assessed from appearance of the milk and udder, respectively, with a score of 0 = normal and 3 = severe. Accelerometers attached to the hind leg recorded lying duration (h/d) and mean bout duration (min/bout). Data were summarized by 24-h period starting at 0900 h using the mean SCC, MS, and US for each d 0–3 d post-challenge and the recorded daily score from d 4–7. Data were analyzed using a regression model in SAS (v9.4) to determine the relationship between the independent variables of SCC, MS, and US and the dependent variables of daily lying duration and mean bout duration. MS was positively associated with mean bout duration (P = 0.005; R² = 0.04; y = 6.4x+72.6), but SCC (P = 0.74) and US (P = 0.26) were not. SCC (P = 0.74), MS (P = 0.73), and US (P = 0.94) were not associated with daily lying time. Of the 3 severity measures, MS was the most sensitive (or most closely associated) with sickness-related behavior and offers the greatest potential to predict clinical mastitis caused by S. uberis. The positive relationship between MS and mean bout duration most likely is driven by the strength of the acute inflammatory response, which results in a more systemic response best represented by these 2 measures. Closer examination of the timing of these events relative to each other within and across cows can potentially improve the ability to predict future cases of clinical mastitis through changes in lying behavior.