Aim of this review was to evaluate the methods of pain measurement used in controlled clinical trials in oncology published within the 1999-2002 period. An electronic literature search strategy was used according to established criteria. Medline data base and PubMed search engine were used. Articles were selected in order to include only studies which had chronic cancer pain as primary or secondary objective of a controlled clinical trial. A specific evaluation scheme was used to examine how pain measurement methods were chosen and implemented in the study procedures. The search strategy identified 68 articles eligible for evaluation. Most articles (69%) chose unidimensional pain measurement tools such as visual analogue scales, numerical rating scales and verbal rating scales while others used questionnaires. The implementation of the pain assessment method was often problematic in many studies especially as to time frame of pain assessment (not specified in 70% of studies), administration modalities (not specified in 45%) and use of non validated measurement methods (15% of studies). Design of study and data analysis were often unclear about the definition of pain outcome measure (40%), patient's compliance with pain assessment (reported only in 1 case), and impact of missing data (75%). Statistical techniques were seldom appropriate for the type of data collected and often inadequate to describe the pain variable under study (41%). It is clear from this review that although most Authors were aware of the need of valid pain measurement tools to be used in clinical trials, too often these tools were not appropriately used in the trial or at least their use was not described with sufficient accuracy in the trial methods.