Objective: To standardize and assess the reliability of ultrasonographic assessment of inflammatory and structural lesions in patients with hand osteoarthritis (OA). Methods: The Outcome Measures in Rheumatology Ultrasound Working Group selected synovial hypertrophy (SH), joint effusion (JE), and power Doppler (PD) signals as the main inflammatory lesions in hand OA, and suggested osteophytes in the scapho-trapezio-trapezoid (STT) and cartilage defects in the proximal interphalangeal (PIP) joints as novel additions to previous structural scoring systems. A complementary imaging atlas provided detailed examples of the scores. A reliability exercise of static images was performed for the inflammatory features, followed by a patient-based exercise with 6 sonographers testing inflammatory and structural features in 12 hand OA patients. We used Cohen's kappa for intrareader and Light's kappa for interreader reliability for all features except PD, in which prevalence-adjusted bias-adjusted kappa (PABAK) was applied. Percentage agreement was also assessed. Results: The web-based reliability exercise demonstrated substantial intra- and interreader reliability for all inflammatory features (κ > 0.64). In the patient-based exercise, intra- and interreader reliability, respectively, varied: SH κ = 0.73 and 0.45; JE κ = 0.70 and 0.55; PD PABAK = 0.90 and 0.88; PIP joint cartilage κ = 0.56 and 0.45; and STT osteophytes κ = 0.62 and 0.36. Percentage close agreement was high for all features (>85%). Conclusion: With ultrasound, substantial to excellent intrareader reliability was found for inflammatory features of hand OA. Interreader reliability was moderate, but overall high close agreement between readers suggests that better reliability is achievable after further training. Assessment of osteophytes in the STT joint and cartilage in the PIP joints achieved less reliability and the latter is not endorsed.