BACKGROUND: Limited joint mobility in diabetic patients has been identified as a risk factor in the development of plantar ulcers. We examined dorsal mobility and passive first ray stiffness in patients with diabetes and investigated the relationship between first ray mobility and ankle joint dorsiflexion. METHODS: Forty individuals were studied: 20 with diabetes (mean estimated duration of 16 +/- 10 years) and 20 matched controls. Dorsal first ray mobility was measured using a mechanical device. Force-vs-dorsal mobility displacement values were collected at 10 N increments to a load limit of 55 N. Ankle joint dorsiflexion motion was measured with a goniometer. The "prayer sign," a clinical indicator of limited joint mobility, was evaluated in each patient. Subjects were separated into the two groups for data analysis. RESULTS: Patients in the diabetic group had more stiffness and less dorsal first ray mobility than the control group (p <.05). In particular, patients with a positive prayer sign had significant first ray stiffness (p <.05). Patients with diabetes also had less ankle dorsiflexion (p <.05). CONCLUSION: Patients with diabetes have more stiffness and less first ray mobility and less ankle dorsiflexion than those without diabetes. The presence of a positive prayer sign correlates with stiffness and loss of first ray mobility. Soft-tissue stiffness may contribute to the development of foot ulcers in diabetic patients with neuropathy.