Introduction: Disease behaviour may guide diagnosis and treatment decisions in patients with interstitial lung disease (ILD). STARLINER aimed to characterise disease behaviour in patients with suspected ILD during the peri-diagnostic period using real-time home-based assessments. Methods: STARLINER (NCT03261037) was an international, multicentre study. Patients ≥ 50 years old with suspected ILD were followed throughout the peri-diagnostic period, consisting of a pre-diagnostic period (from enrolment to diagnosis) and a post-diagnostic period (from diagnosis to treatment initiation). Study length was variable (≤ 18 months). The primary endpoint was time-adjusted semi-annual forced vital capacity (FVC) change measured during the peri-diagnostic period using daily home spirometry in patients with idiopathic pulmonary fibrosis (IPF). Secondary outcomes included changes in FVC (home spirometry) in patients with non-IPF ILD, changes in FVC (site spirometry), changes in physical functional capacity measured by daily home accelerometry and site 6-min walk distance (6MWD), and changes in patient-reported outcomes (PROs) in IPF or non-IPF ILD. Results: Of the 178 patients enrolled in the study, 68 patients were diagnosed with IPF, 62 patients were diagnosed with non-IPF ILD, 9 patients received a non-ILD diagnosis and 39 patients did not receive a diagnosis. Technical and analytical issues led to problems in applying the prespecified linear regression model to analyse the home FVC data. Time-adjusted median (quartile [Q]1, Q3) semi-annual FVC change during the peri-diagnostic period measured using home and site spirometry, respectively, was – 147.7 (– 723.8, 376.2) ml and – 149.0 (– 314.6, 163.9) ml for IPF and 19.1 (– 194.9, 519.0) ml and – 23.4 (– 117.9, 133.5) ml in non-IPF ILD. A greater decline in steps per day was observed for IPF versus non-IPF ILD, whereas an increase in 6MWD was observed for patients with IPF versus a decline in 6MWD for patients with non-IPF ILD. No clear patterns of disease behaviour were observed for IPF versus non-IPF ILD for PROs. Conclusions: Despite home spirometry being feasible for most patients and centres, technical and analytical challenges in the home-based assessments prevented firm conclusions regarding disease behaviour. This highlights that further optimisation of the technology and analysis methods is required before widespread implementation. Trial Registration: NCT03261037.