The objective was to use longitudinal data of blood nonesterified fatty acids (NEFA) and β-hydroxybutyrate (BHBA) concentrations to describe the relationship between NEFA and BHBA in dairy cows during the periparturient period. Blood NEFA and BHBA concentration data collected from d −21 prepartum to 21 postpartum for 269 multiparous Holstein cows were recruited from 4 different studies carried out within our research groups. Of the 269 cows enrolled in the data set, 117 cows (43.5%) had at least 1 postpartum hyperketonemic event (BHBA ≥ 1.2 mmol/L), and 202 cows (75.1%) had at least 1 event of elevated postpartum NEFA (≥700 µEq/L) between 3 and 21 d in milk. Area under the curve (AUC) was used to investigate relationships between metabolites over time. Overall, Pearson correlation relationships between transition period NEFA and BHBA AUC were poor. There was a negative correlation between postpartum NEFA AUC and prepartum BHBA AUC, although the correlation coefficient was low (r = −0.26). A positive correlation existed between postpartum NEFA AUC and postpartum BHBA AUC; however, the correlation coefficient was low (r = 0.26), reinforcing a poor relationship between these metabolites during the periparturient period. Large variation was found between the day of maximum NEFA concentration within the first 21 d in milk and day of maximum BHBA concentration for the same time period. The mean and median days of maximum NEFA concentration were 6.8 and 6 d, respectively, whereas the mean and median days of maximum BHBA concentration were 9.6 and 8 d, respectively; however the range in days for both the mean and median day of maximum concentrations was very large. Overall, our data set indicates a poor relationship between blood concentrations of NEFA and BHBA during the periparturient period of dairy cows, suggesting that elevated concentrations of one should not be extrapolated to suggest elevated concentrations of the other metabolite.