This paper employs the time-series negative binomial regression model (TNBM) to test the hypothesis effects of purchasing power parity (PPP) theory on the counts data of visitors to the north-west of Sweden (SW6 region). We consider a sample of monthly time-series count data from 1993:01 to 2008:12 taken from five countries: Denmark, the United Kingdom, Switzerland, Japan and the United States. For each visiting country, we specify separate equations by including the relative available information. We then estimate these equations using the time - series negative binomial model (TNBM). The benefit of this model is that it is much more flexible and therefore likely to fit better (if the data is not Poisson distributed) and hence is more efficient than single-equation estimation methods such as least squares. We found that the number of visitors to Sweden is negatively related to the absolute PPP and relative PPP. This result is in accordance with macroeconomic theory and the PPP theory. The results also show that some lagged dependent variables, and several monthly dummies (representing seasonal effects), have a significant impact on the number of visitors to north-west Sweden. We also find that, in at least some cases, absolute PPP, relative PPP and relative price have significant effects on international tourism demand.