To determine the frequency of critical radiology results in 9.3 million radiology reports from our health system, to identify those containing documentation of communication by using automated text-classification algorithms, and to assess the impact of a policy requiring documentation of critical results communication. This HIPAA-compliant retrospective study received institutional review board approval. Text-mining algorithms that were previously validated to have mean accuracies of more than 90% for identifying certain critical results and documentation of communications were applied to a database of 9.3 million radiology reports. The frequency of critical results and documentation of communication were then determined from 1990 to 2011. There was an increase in documentation of communication for all critical results from 1990 to 2011. In 1990, 19.0% of reports with critical values had evidence of documentation of communication compared with 72.4% of reports in 2010. The linear trend for increasing documentation of communications began in 1997 and continued until 2011 (P < .001). From 1990 to 2011, documentation of communication was highest in acute scrotal torsion (70.6%) and ectopic pregnancy (65.4%) and lowest in unexplained free-intraperitoneal air (29.5%) and malpositioned tubes (30.4%). In 2010-2011, radiologists were least likely to document communication of results for malpositioned endotracheal and enteric tubes (2010, 58.56%; 2011, 57.50%) and unexplained free-intraperitoneal air (2010, 59.57%; 2011, 75.51%). They were most likely to document communication of results for ectopic pregnancy (2010, 94.12%; 2011, 93.48%) and acute appendicitis (2010, 86.87%; 2011, 84.31%). There was an increase in documentation of communication of critical results, which demonstrated a rising linear trend that began in 1997 and continued until 2011. The increasing trend began well before policy implementation, indicating that other factors such as heightened awareness among radiologists likely had a role.