Privacy-preserving data mining techniques could encourage health data custodians to provide accurate information for mining by ensuring that the data mining procedures and results cannot, with any reasonable degree of certainty, violate data privacy. We outline privacypreserving data mining techniques/systems in the literature and in industry. They range from privacy-preserving data publishing, privacypreserving (distributed) computation to privacy-preserving data mining result release. We discuss their strength and weaknesses respectively, and indicate there is no perfect technical solution yet. We also provide and discuss a possible development framework for privacy-preserving health data mining systems.