This paper examines the sensitivity and precision of Medline searching for randomised clinical trials (RCTs). It compares Medline search results with a "gold standard" of known RCTs published in 1988 in ophthalmology and other medical fields. The study found that Medline searches had a sensitivity of 82% for ophthalmology RCTs in 1988, but overall sensitivity across all studies was 51%, 77%, and 63% for different gold standards. The precision of Medline searches was 8%, with a median of 32.5%. The study highlights the need for improved indexing and registration of RCTs to enhance search accuracy. It also notes that many RCTs are not indexed in Medline, and that some trials published before 1966 or in non-Medline journals are not included in the system. The paper emphasizes the importance of using appropriate search strategies, including subject terms, truncation, and free-text terms, to improve search sensitivity and precision. It also discusses the challenges of identifying unpublished trials and the need for systematic reviews to include all relevant studies. The study concludes that while Medline indexing has improved, sensitivity remains unsatisfactory, and a mechanism is needed to "register" known trials for better data collection. The paper also provides a detailed Medline search strategy for identifying RCTs, including specific terms and combinations to enhance search effectiveness. The study underscores the importance of comprehensive and unbiased data collection for systematic reviews and highlights the need for improved indexing and registration systems to ensure all relevant trials are included.This paper examines the sensitivity and precision of Medline searching for randomised clinical trials (RCTs). It compares Medline search results with a "gold standard" of known RCTs published in 1988 in ophthalmology and other medical fields. The study found that Medline searches had a sensitivity of 82% for ophthalmology RCTs in 1988, but overall sensitivity across all studies was 51%, 77%, and 63% for different gold standards. The precision of Medline searches was 8%, with a median of 32.5%. The study highlights the need for improved indexing and registration of RCTs to enhance search accuracy. It also notes that many RCTs are not indexed in Medline, and that some trials published before 1966 or in non-Medline journals are not included in the system. The paper emphasizes the importance of using appropriate search strategies, including subject terms, truncation, and free-text terms, to improve search sensitivity and precision. It also discusses the challenges of identifying unpublished trials and the need for systematic reviews to include all relevant studies. The study concludes that while Medline indexing has improved, sensitivity remains unsatisfactory, and a mechanism is needed to "register" known trials for better data collection. The paper also provides a detailed Medline search strategy for identifying RCTs, including specific terms and combinations to enhance search effectiveness. The study underscores the importance of comprehensive and unbiased data collection for systematic reviews and highlights the need for improved indexing and registration systems to ensure all relevant trials are included.