Screening for cancer has become a standard of practice in contemporary health care. Screening tests are often ordered routinely, without discussion of risks and benefits. For clinicians who want to inform patients and undertake shared decision-making, the goal of effective communication presents a number of challenges. To begin with, the probabilities to be discussed are small. For each screening test done, the chance of finding and effectively treating an early cancer is quite low. Likewise, the chance of causing harm, such as a false positive screen followed by an invasive test resulting in complications, is also very unlikely but possible. Using accurate terms that patients can understand is only the first step, however, as the decision-making process should take into account the patient's perceptions, values, and preferences. This paper briefly reviews the current state of evidence for prostate, colon, and breast cancer screening, then outlines several strategies toward effective clinical communication. The concepts of absolute risk, relative risk, and number needed to screen are reviewed. Natural frequency presentation, a relatively new method for portraying benefits and harms, is introduced and encouraged, as recent evidence suggests that natural frequencies are better understood and are more concordant with patients' values than alternative formats.