The present invention relates to methods of diagnosing bladder cancer in a patient, involving determining the methylation status of Methylation Variable Positions (MVPs) in DNA from the patient and providing a diagnosis based on methylation status data. The invention also relates to methods of treating bladder cancer comprising providing a diagnosis of bladder cancer by the diagnostic methods defined herein followed by administering one or more anti-cancer agents to a patient. The invention also relates to methylation-discriminatory arrays comprising probes directed to the MVPs defined herein and kits comprising the arrays.