AbstractObjective:To investigate differences in orbital involvement in patients with invasive versus non-invasive fungal sinusitis.Method:One hundred consecutive cases of fungal sinusitis were assessed clinically and by computed tomography scan to evaluate orbital involvement.Results:Clinical orbital involvement was more common in invasive (73.5 per cent) than non-invasive (12.1 per cent) fungal sinusitis (p = 0.000). Computed tomography scanning showed similar orbital involvement in both groups, except for erosion of the floor of the orbit, which was more common in patients with invasive fungal sinusitis (p = 0.01). Extra-ocular muscle enlargement (44.4 vs 4 per cent, p = 0.01) and optic atrophy (44.4 vs 0 per cent, p = 0.003) were more common in chronic than acute invasive fungal sinusitis. Four patients (16 per cent) with acute invasive fungal sinusitis had no evidence of orbital involvement on scanning, despite clinical evidence of optic atrophy.Conclusion:Orbital involvement is more common in invasive than non-invasive fungal sinusitis. The difference is more evident clinically than on computed tomography scanning. Patients with acute invasive fungal sinusitis may have limited evidence of orbital involvement on scanning, despite extensive clinical disease.