To judge the influence of speaker background on the quality of five Standard Dutch long vowels and diphthongs, the spectra of these vowel realizations in the spontaneous speech of 70 subjects were measured and analyzed with regard to the subjects’ age, sex, regions of education and residence, and their level of education and occupation. Besides the level of education /occupation, the factor ’age group’ had a major effect on the variations in speech production. The vowel attributes ’onset’ and ’degree of diphthongization’ were affected differently. Highly educated speakers of the younger and middle-aged generation displayed systematic age patterns; lowly educated speakers and the older generation did not. A slight effect of region of residence was found for some females. An effect of sex was found for the higher educated speakers of the youngest age group. The vowel variations that were related to age reflected several pronunciation changes in progress.