The aim of this study was to develop a questionnaire to evaluate rapid weight loss patterns of competitive judo players and to assess its validity and reliability. We evaluated the reliability (n=94), content validity (evaluation by 10 experts), discriminant validity (differences in scores between athletes with body weight below and above their weight class; n=100) and convergent validity (correlation with Restraint Scale; n=60). No item was considered unclear or ambiguous by more than 20% of the experts. The intraclass Coefficient Correlation was above 0.90 for all questions whose answers were parametric (P<0.001; n=94) and no significant differences were found between test and retest scores (n=94--Wilcoxon's signed rank test). Cronbach's alpha was 0.98 for scores obtained between test and retest. Non-numerical questions showed proportions of agreement >80%; Spearman's Correlation between the Restraint Scale and the Rapid Weight Loss Questionnaire was 0.62 (P<0.001; n=60). Athletes below their weight class (n=50) had a significantly lower score compared with athletes above the weight class (n=50; P<0.001--Mann-Whitney U test). In conclusion, the questionnaire showed good validity and reliability and could be used accurately to assess weight loss patterns of judo players.