The objective of this study is to assess the reliability of clinical examination in patients with erosive osteoarthritis (EOA). Eighteen patients with EOA underwent clinical examination for joint tenderness, bony swelling, and inflammation by two independent, blinded assessors. All patients were also examined by ultrasound (US) by an independent radiologist. The inter-observer agreement was moderate for bony swelling and joint tenderness and fair for joint inflammation (kappa = 0.513, 0.448, and 0.402, respectively). US detected significantly more inflamed joints than clinical examination. The sensitivity and specificity of clinical examination for joint inflammation were 0.12 and 0.95, respectively. Clinical joint counts for bony swelling, tenderness, and inflammation all correlated with functional status, assessed by the functional index for hand osteoarthritis (FIHOA), whereas US joint counts for joint inflammation did not correlate with the FIHOA. No correlation was found between any clinical or US joint count and visual analog scale for pain. US detects more joints with inflammation than clinical examination in patients with EOA. US can supplement the clinical examination of patients with EOA, as US-detected subclinical joint inflammation might accelerate joint damage and thus functional impairment.