Understanding changes of behavioral parameters recorded by automated health monitoring systems based on ear-attached sensors on the days immediately before and after diagnosis of metritis and clinical mastitis can help develop dairy cow health monitoring and management strategies. Therefore, the objective of this observational cohort study was to characterize rumination time, physical activity, and lying time monitored by an ear-attached sensor immediately before, during, and after clinical diagnosis (CD) of metritis and clinical mastitis. Lactating Holstein cows monitored daily for up to 21 DIM for detection of health disorders were retrospectively included in the no-clinical health disorder group (NCHD; n = 616) if no clinical health disorders were diagnosed. Cows were included in the metritis (MET; n = 69) or clinical mastitis (MAST; n = 36) group if diagnosed only with non-severe metritis (i.e., no systemic signs of disease) or clinical mastitis (i.e., no pyrexia and no systemic signs of disease), respectively. Cows diagnosed with severe metritis (i.e., systemic signs of disease) or clinical mastitis (i.e., pyrexia and systemic signs of disease), or cows diagnosed with non-severe metritis or clinical mastitis plus another clinical disorder within -7 to +7 d of CD of metritis or clinical mastitis diagnosis were included in the metritis plus (MET+; n = 25) or the clinical mastitis plus (MAST+; n = 15) group, respectively. All cows were fitted with an ear-attached accelerometer to measure rumination time, physical activity, and lying time. Data were summarized as mean daily values, mean value absolute change, and relative change for the mean daily value from 3 or 5 d before CD to the nadir for cows with metritis and clinical mastitis, respectively. Data were analyzed with linear mixed models with or without repeated measures as appropriate. Rumination time and physical activity were lesser, and lying time was greater for the MET and MET+ groups than for the NCHD group for most days from -4 to +7 d of CD of metritis. Generally, daily rumination time, physical activity, and lying time differences were larger and more prolonged between the MET+ and NCHD groups than between the MET and NCHD groups. Similarly, cows in the MAST and MAST+ groups had lesser rumination time and physical activity than cows in the NCHD group for several days before diagnosis of clinical mastitis. Lying time was greater for the MAST+ than the NCHD group on day -1 and 0 relative to CD, but there were no differences with the MAST group. Absolute values and relative changes from 3 d before CD to the day of the nadir for rumination time and physical activity, or peak for lying time were different for cows in the MET and MET+ groups than for the NCHD group. Similar results were observed for the MAST and MAST+ groups compared with the NCHD group. For cows affected by metritis, either an increase in rumination time and physical activity or a decrease in lying time was observed from the day of CD to resolution of clinical signs but no changes were observed for the NCHD. Similarly, cows with clinical mastitis and the NCHD group had different rumination time, physical activity, and lying time on the day of CD and resolution of clinical signs, but cows with clinical mastitis had no significant changes from the day of CD to resolution of clinical signs. We conclude that dairy cows affected by metritis and clinical mastitis presented substantial alterations of the pattern of rumination time, physical activity, and lying time captured by an ear-attached sensor. Thus, automated health monitoring systems based on ear-attached sensors might be used as an aid for identifying cows with metritis and clinical mastitis. Moreover, rumination time, physical activity, and lying time changes after CD might be good indicators of resolution of clinical signs of metritis but not mastitis.