OBJECTIVES: Over 40 states have prescription drug monitoring programs (PDMP) to monitor the utilization of controlled substances (CS) with the goal of reducing drug abuse and diversion. Little is known about how PDMPs are actually used by health care professionals. The purpose of this paper is to review how prescribers utilize PDMPs and to assess the impact of a PDMP on CS prescribing. METHODS: The paper uses data from the Kentucky All Schedule Prescription Electronic Reporting Program (KASPER) from 2002-2009.  We review CS prescribing and KASPER utilization using descriptive statistics, visualization, and t-test, controlling for characteristics of KASPER users, the number of KASPER requests for each user type, and geographic distribution.  Statistical analysis is conducted in STATA v11.0. RESULTS: CS prescriptions issued by Kentucky prescribers increased from 8.4 million in 2002 to over 11 million in 2009.  During this period, KASPER system requests increased from 100,000 in 2002 to more than 530,000 in 2009.  Yet, most CS prescribers (64%) do not have KASPER accounts.  Comparing KASPER users across geographic regions, rural areas have a higher (49%) rate of KASPER use than urban areas (32%, p<.05).  For CS prescribing, the typical KASPER account holder issued 1,665 prescriptions a year in 2009, compared to 250 prescriptions issued by non-account holders.  The top CS prescriber in 2009 issued over 41,000 prescriptions, an increase of 60% from the top prescriber in 2005. Finally, CS prescribing has become skewed, with 10% of prescribers issuing 95% of all CS prescriptions. CONCLUSIONS: Since 2004, CS prescribing in Kentucky has increased by 40% and KASPER system requests have increased by 400%. The most interesting finding is that the majority of growth in CS prescribing is from a relatively small number of prescribers.   Whether this finding is a direct result of the PDMP is a question for further research.