Abstract： Objective To estimate the value of clinical parameters (such as patients' age,longitudinal melanonychia width and location) for the differential diagnosis of malignant and benign longitudinal melanonychia as well as for the evaluation of the necessity for invasive management.Methods A retrospective study was performed on 28 cases of subungual malignant melanoma collected from 2000 to 2010 as well as on 62 cases of benign longitudinal melanonychia from 2005 to 2010.Clinical analysis was carried out to compare the differences in clinical parameters such as.patients' age,longitudinal melanonychia width and lesional location,between the malignant melanoma and benign longitudinal melanonychia cases.Logistic regression analysis and ROC method were used to determine valuable clinical parameters for the differential diagnosis of malignant and benign longitudinal melanonychia.Results Significant differences were observed in the median age at diagnosis (23.0 years vs.52.5 years,Z =5.44,P ＜ 0.01 ),age at onset (21.0 years vs.48.0 years,Z =4.70,P ＜ 0.01 ),and longitudinal melanonychia width (3.0 mm vs.15.0 mm,Z =5.69,P ＜ 0.01 ) between the patients with malignant melanoma and benign longitudinal melanonychia.The involvement of thumb and hallux was observed in 77.8％ of the subungual melanoma cases,and 48.3％ of the benign cases (x2 =6.57,P ＜ 0.05).ROC method and Logistic regression analysis indicated that the age at onset and diagnosis as well as width of longitudinal melanonychia were of diagnostic value for the differential diagnosis of malignant and benign longitudinal melanonychia.Conclusions Not all longitudinal melanonychia cases need an invasive management at the time of awareness.The age at onset and diagnosis,width of melanonychia and site of the onset appear to be valuable in the differential diagnosis of malignant and benign longitudinal melanonychia,and there is a possibility to guide clinical diagnosis and treatment by establishing a mathematical model with these parameters.