Prenatal drug exposure is an important pediatric health issue. However, the effects on children are not clear because of limitations in the way drug exposure is typically measured. For example, one cannot say cocaine causes a specific outcome if cocaine exposure is not measured accurately. Before we can determine the developmental outcomes associated with drug exposure, 4 measurement issues must be considered: (1) the amount of exposure varies greatly, such as from 1 to 709 g of crack per month; (2) exposure may vary by trimester; (3) exposure could be to one drug or multiple drugs; and (4) different sources of exposure data can be inconsistent (e.g., toxicology and maternal self-report). We use data from 248 families participating in an ongoing longitudinal study to provide concrete examples of these measurement issues. Both nursing researchers and practitioners must carefully attend to measurement issues when interpreting research on the effects of prenatal drug exposure.