The relationships between direct-to-consumer advertising expenditures and the monthly frequencies of diagnoses and prescriptions written associated with the products advertised are examined. The analyses utilized quasi-experimental time-series techniques. Data from the National Ambulatory Medical Care Survey and Competitive Media Reporting were used to calculate monthly levels of the dependent and independent variables. The dependent variables included monthly frequencies of diagnoses for the products' FDA-approved indications, medications prescribed within the advertised pharmaceutical class, and medications prescribed for the specific advertised agent. The independent variables included monthly expenditures for advertising each pharmaceutical class and each specific agent. Several significant monthly relationships were found. The diagnoses of hyperlipidemia (p = 0.008) and the number of prescriptions written for antilipemics (p = 0.003) were positively associated with the advertising expenditure for antilipemics. The number of prescriptions written for Claritin (p = 0.004) and Zocor (p < 0.001) was positively related to the advertising expenditure for their respective pharmaceutical classes; the amount of prescriptions written for Hismanal (p = 0.007), Seldane (p < 0.001), and Zantac (p = 0.004) was negatively related to the advertising expenditure for their respective pharmaceutical classes. The number of prescriptions written for Claritin (p = 0.005) and Zocor (p < 0.001) was positively related to the advertising expenditure for each specific product; the amount of prescriptions written for Hismanal (p = 0.049) was negatively associated with the amount of money spent specifically advertising the agent. No significant associations were found in antihypertensive drugs and drugs to treat benign prostatic hypertrophy. The results of the analyses suggest that the direct-to-consumer advertising expenditure is associated with physician diagnosing and physician prescribing for certain drugs and drug classes.