A thermorhythmometric analysis was carried out on data from a patient who underwent a prophylactic subcutaneous mastectomy, subsequently to a preoperative mammogram revealing clustered small calcifications in the left breast. The patient self-measured surface temperature of each breast, above and below the nipple, at intervals of 75 +/- 10 min for 59 h while awake. In one location of each breast, the recording thermistor-probe was insulated for 21.5 h while other probe locations remained uninsulated. The overall rhythm-adjusted average surface temperature and the extent of predictable circadian variation differed with statistical significance when the two breasts were compared. The left breast exhibited a higher rhythm-adjusted mean temperature and a lower extent of predictable circadian variation, as compared to the contralateral breast. The interbreast differences of surface temperature also demonstrated a statistically significant rhythm. A review on results of rhythmometry of breast temperature was also carried out. The thermorhythmometric findings here reported must not necessarily be regarded as indicative of cancer; they may be found in non-cancerous subjects and may or may not reflect early pathology. The objective of this publication is to suggest that non-invasive mammary thermorhythmometry may complement clinical histopathology. This subject may exemplify a new principle awaiting scrutiny with much more extensive sampling and much longer follow-up, namely that chronopathology including chronoprotopathology, alongside established diagnostic procedures, may provide an indication for prophylactic intervention.