Purpose To quantify the central attention-diverting effect of hands-free cellular phone conversation on visual field awareness. Design Experimental study. Methods Twenty male and 21 female healthy participants performed a pretest and baseline Esterman visual field examinations with the Humphrey Systems Visual Field Analyzer II. During the consequent third examination, each participant engaged in a hands-free conversation using a cellular phone. The conversation was the same for all participants. Visual field performance parameters were compared between the second (baseline) examination, and the third (test) examination for each eye. Results During phone conversation, missed points increased from mean 1.0 ± 1.5 to 2.6 ± 3.4 (P ≤ .001) in the right eye and from 1.1 ± 1.53 to 3.0 ± 3.4 (P < .001) in the left eye. Fixation loss increased from mean 7.8% to 27.4% (P < .0001) and from 7.2% to 34.8% (P < .0001) for the right and left eyes, respectively. Test duration increased by a mean of 0.28 seconds (15%) per stimulus (P < .0001). Approximately half of missed points were inside the central 30 degrees. There was no significant difference in the performance of male and female participants. Conclusion We describe a new model for the quantification of the attention-diverting effect of cellular-phone conversation on the visual field. In the current study, cellular hands-free conversation caused some subjects to miss significantly more points, react slower to each stimulus, and perform with reduced precision. Legislative restrictions on concomitant cellular-phone conversation and driving may need to be based on individual performance rather than a general ban on cellular phone usage.