This paper presents the results of research on local air pollution (nitrogen and sulfur concentrations) and on the changes in the health status of trees observed in spruce stands in the period 1980–2011 in the Krkonoše Mountains National Park. Data on precipitation and sulfur and nitrogen deposition were collected in regular 2-week intervals from 1994 to 2010. Precipitation was measured at 5 monitoring stations; the health status of forest stands was evaluated on 6 research plots located in stands dominated by Norway spruce (Picea abies [L.] Karst) in zones where there has been a significant threat from air pollution since 1980. The health status of spruce stands was assessed on the basis of the degree of defoliation, classified into 6 levels. In all localities since 1994, the total deposition of sulfates decreased significantly, from 50–80 kg ha⁻¹ year⁻¹ to 8–13 kg ha⁻¹ year⁻¹; however, no clear trend in the development of nitrogen deposition could be stated. The mean defoliation of living and all trees was 32% (± 0.5 SE) and 63% (± 0.8 SE), respectively, on plots with autochthonous stands, and 91.5% (±5.8 SE) and 97.6% (±1.7 SE), respectively, on a plot with an allochthonous stand. The defoliation of living and all trees differed across research plots. Despite a negative relationship between defoliation of all trees on plots and atmospheric deposition of sulfur (P  =  0.012; r  =  −0.25), air pollution in the Sudeten still represents a serious hazard for the forest ecosystem. This relationship differed across research plots (F[5, 96]  =  110, P < 0.001). Close-to-nature management techniques aimed at the enhancement of forest complexity and preferential use of autochthonous populations of trees in timely regenerated forest stands may be of crucial importance for the restoration and preservation of these mountain forest ecosystems.