The Italian External Quality Assessment scheme for fragile X syndrome started in 2001 as an activity funded by the National Health System and coordinated by the National Institute of Public Health. The aim of this work is to present the data of 5 years (2001--2004 and 2006) of survey. The External Quality Assessment scheme was designed to cover the following points: (a) genotyping and (b) interpretation and reporting of results. Overall, the scheme covered about 65% of all Italian public laboratories. The average reporting of results was 91.6%, with an overall success rate of 76%. The rate of diagnostic errors observed was on average 5%. Inaccuracy in sizing of CGG repeats of normal and premutated alleles was reported. During the survey the proportion of laboratories using a Southern blotting, polymerase chain reaction, and ABI sizing kit in combination rose from 36.8% to 70.6%. The reports from laboratories showed incompleteness and considerable variations in expected outcomes. For this reason, in 2004 a model for written reports was introduced. In conclusion, these data underscore the need to participate in External Quality Assessment schemes as an educational resource to ensure quality in molecular genetic testing.