Ultraviolet radiation (UVR) is the principal environmental cause of skin cancer and can be greatly reduced through environmental, structural and behavioral modifications. Studies that measured the effectiveness of various environmental and behavioral interventions on reducing personal UVR exposure largely have relied upon self-report, which may be distorted by recruitment bias, recall error and social desirability. A small number of studies have used objective measures, but these measures have tended to be costly or labor intensive. The development of a reliable, cost-effective, rapid and systematic observational measure for quantifying physical activity in children within specific settings such as schools and recreation areas has been developed and validated. The potential exists to develop a similar instrument for sun protection, providing a valid and reliable measure of sun protection and exposure within specific outdoor environments. Several settings including schools, beaches, swimming pools, and outdoor recreation sites are high risk areas for sun exposure. The development of valid, reliable, and efficient observational instruments to measure sun protection would assist in evaluating the effectiveness of environmental, structural and behavioral strategies implemented within these settings. We propose to develop an observational instrument to systematically measure sun protection in various outdoor settings. Momentary ecological time sampling will be used to assess gender, head wear, sunglasses use, upper body covering, lower body covering and shade use. Validity will be assessed by comparing the observations to a videotape (i.e., gold standard). Inter-rater reliability will be assessed by using multiple observers. Personal Digital Assistants will be compared to pencil and paper methodologies to assess respondent burden and error rate. Instruments will be developed and field tested in Honolulu, Hawaii. If shown to be valid, reliable and feasible, this measurement system will make an important contribution to skin cancer prevention research.