Over the years, much effort has been put into mastitis control programs. To further improve such programs, we need to understand farmers’ knowledge, attitude and behavior regarding udder health, and the way this can be influenced by mastitis control programs. This study aimed to explore the effect of a Dutch national mastitis control program on farmers’ knowledge, attitude and behavior regarding mastitis. In this study, 204 randomly selected dairy farmers completed a survey on attitude, knowledge and behavior regarding mastitis before the start of the national mastitis control program (2004) and in the final year of the program (2009). Statistical analyses show that, compared to 2004, the attitude, knowledge and behavior of the participating farmers changed significantly. Farmers’ satisfaction level and problem level of BMSCC changed; farmers were satisfied with on average 156,000 cells/ml in 2004 compared to 150,000 cells/ml in 2009, and perceived a problem at 285,000 cells/ml in 2004 compared to 271,000 cells/ml in 2009. More farmers perceived that they had sufficient knowledge about the control of mastitis (34% in 2004 vs. 53% in 2009), and they focused more often on udder health characteristics when selecting bulls (46% vs. 61%). Specific mastitis control measures have increased significantly during the program. The use of milking gloves increased from 15% to 46%, the use of a standardized mastitis treatment protocol increased from 7% to 34% and cubicles are cleaned more often (2.28 vs. 2.51 times/day).