This paper presents an empirical study of the validity and reliability of a new method to quantify hoarseness or roughness of the voice by measuring vocal jitter which refers to the temporal irregularities of the vibration process of the vocal folds. Whereas it is quite possible to measure jitter in recordings of sustained vowels elicited in laboratory conditions, there seems to be no reliable method of measuring it in connected speech. This problem arises in forensic speaker identification (S I), where speech samples from non-cooperative speakers have to be analysed . Therefore a new jitter-algorithm which was specifically developed for application in forensic SI is rested. Seven male German speakers with different kinds of pathological hoarseness and seven speakers with normal voices served as subjects. The results show that the algorithm reliably measures jitter not only based on isolated vowels bur also based on vowels in connected speech, thus allowing for quantification of an additional parameter in forensic SI.