This study addresses two questions: (1) What effect does quality improvement have on satisfaction with public transport services? (2) What effect does quality improve~ ment have on passengers' perceived frequency of negative critical incidents? A repre~ sentative sample was used of people 16 to 75 years old in the 13 regions in Sweden that were conducting quality improvements in public transport. Data were collected before and after implementation (n=2797). The before and after samples consisted of independent groups of respondents. The response rate was 54 percent. The main conclusion of the study is that the satisfaction people experience when using public transport services is influenced by quality improvements only to a limited extent. Furthermore, the effect was directionally opposite in that respondents reported Jess satisfaction and higher frequencies of negative critical incidents after the quality improvements had been implemented.