Phi, the ratio of 1:1.6, is present in nature. This study examined the diagnostic potential of handwriting by determining whether phi was exhibited in individuals’ handwriting. Handwriting samples were gathered from archived writings by five criminals and five non-criminals. Lower, middle, and upper zone heights of the samples were measured. Zonal proportions were calculated as ratios among the letter heights for each zone. The non-criminal group’s zonal ratio was 1.66, which a t-test showed to be statistically equal to phi. The criminal group’s zonal ratio was 3.51, which a t-test showed to be significantly different than phi. Zonal proportions within people’s handwriting provide insight into their psychological balance. Psychologically healthier people exhibit proportions close to phi. Therapists may use a client’s handwriting as an indicator of health or therapeutic progress. Future study of handwriting is recommended.