OBJECTIVES: To characterise the clinical characteristics and longitudinal outcomes in primary lateral sclerosis (PLS), including median survival from symptom onset and age at death. METHODS: The authors retrospectively reviewed electronic health records of patients diagnosed with PLS referred to a specialised motor neuron disorders clinic from 2002 to 2024, analysed longitudinal Revised Amyotrophic Lateral Sclerosis Functional Rating Scale (ALSFRS-R) assessments using joint models and used Kaplan-Meier methods and life tables to calculate median survival and age at death compared with population-based values. RESULTS: Of 52 patients, 34 (65%) were male, 41 (79%) first noted symptoms in the lower limbs and 10 (19%) in corticobulbar function. Median age of symptom onset was 53 years. The mean annual rate of functional decline was -1.92 ALSFRS-R points (95% CI -3.03 to -0.78), with equal highest rates of decline in fine and gross motor subscores. Five patients (10%) received gastrostomy and three (6%) non-invasive ventilation. Median survival from symptom onset was 23.1 years (22.7 to not reached), and median age at death was 79.5 years (77.8 to not reached) compared with a population-based reference mean of 81.9 years (81.1 to 82.8). DISCUSSION: PLS may be commensurate with near-normal life expectancy. Significant disability arises from limb motor dysfunction, with a minority of patients requiring nutritional or respiratory support. This has important implications for counselling and trial design.