The neonatal period is very important in calves. It is extremely important to closely monitor newborn calves with good colostrum management during this period. In this study, the aim was to investigate whether the clinical parameters in the first 15 days after calves are born are correlated with diarrhea and whether those values are the early clinical predictors of the diarrhea that will occur in this period and also to investigate the correlation between diarrhea and the failure of transfer of passive immunity (FTPI). Eighty-two Holstein calves were used in the study. The calves were examined systemically every day and were scored according to a standard form. In the first 15 day period, 64.63% of the calves had diarrhea. In diarrheic calves, the most common findings on the previous day without diarrhea were fetid feces (43.40%), changes in the consistency and color of feces, and a decrease in the temperature of the ears (35.85%). According to non diarrheic calves, fetid feces (P < 0.01), changes in the consistency and color of feces, and nasal discharge were more common among diarrheic calves on the day before diarrhea (p < 0.001). The duration of diarrhea in calves with FTPI was longer than without FTPI. As a result, it is important for calves to be monitored daily in the first 15 days, looking for early signs of diarrhea in this period, namely fetid feces and changes in the consistency and the color of the feces. In addition, coexistence of any fecal changes with the decrease in the temperature of the ears may be clinical predictors of diarrhea. As a result of the daily monitoring of the calves, although the morbidity rate was high, none of the animals died.