The purpose of this study was to explore stuttering behaviour associated with word-type and word-frequency in a large group of adults who stutter (AWS). The study method involved analysing spontaneous speech samples of 50 AWS on the following features: 1) the occurrence of stuttering on content and function words, 2) the occurrence of stuttering on function words at the function/content word boundary, 3) the occurrence of syllable repetitions in relation to moments of stuttering on function and content words, and 4) word frequency of stuttered words compared to control words. Results indicated that moments of stuttering occurred more often on content words compared to function words. Furthermore, if stuttering occurred on a function word, it was found to occur most often at the function/content word boundary. No difference was found when the data were further analyzed as a function of frequency of stuttering. The AWS who had a high frequency of stuttering did not differ significantly from those with a low frequency of stuttering. Syllable repetitions occurred more often on function words compared to content words. In general, the AWS who showed a low frequency of stuttering exhibited a higher percentage of syllable repetitions. The word frequency of stuttered versus control words did not differ significantly. There was also no difference in word frequency for stuttered function versus stuttered content words. The results were interpreted to provide general support for the EXPLAN theory of stuttering behaviour proposed by Howell (2004) and colleagues (Howell & Au Yeung, 2002; Howell, Au-Yeung & Sackin, 2000).