Background: The increasing prevalence of specific language impairment (SLI) is a matter of current debate. Aims: Speech and language therapists and other authorities in Finland have discussed the prevalence of SLI since the 1990s. This discussion has been based on international studies because of the lack of national studies. This paper presents the first Finnish prevalence study of SLI in primary healthcare and, thus, participates in the international discussion on the prevalence of SLI. Furthermore, two samples of delayed language development (DLD) were studied. Methods & Procedures: This is a retrospective study from 1989-1999. It was conducted on the population of one of the biggest towns in Finland, and was collected from the statistical records of speech and language therapists. Outcomes & Results: The prevalence of SLI increased, and this increase was statistically significant. The prevalence of SLI was less than 1% in age group 0-6 years and, thus, presents a much lower prevalence than international discussion has suggested. SLI seems to be present particularly in boys though it was also increasing in girls. Furthermore, children with SLI seem to be more affected by receptive difficulties over the period studied. Particularly important is the observation that the prevalence of DLD was also increasing, and together with SLI they suggest a prevalence rate of 2.5% in Finland. Conclusions: The low prevalence of SLI in this study might be a consequence of the path of intervention that effectively separates SLI from delayed language development. Furthermore, the questions of language specific features needs to be emphasized. The findings of this study suggest that the prevalence of SLI increased as did the prevalence of DLD. The range of prevalence estimates of SLI in different studies raises the need for national and international epidemiological studies of SLI with equal criteria of assessment in each language. (Contains 2 figures and 9 tables.)