Tuberous sclerosis complex (TSC) is a genetic disorder associated with mTOR over-activation and disruption of MAPK, PI3K and AMPK signalling. Children with TSC have significant deficits on neuropsychological attention tasks, particularly dual tasking. Here we investigated attentional skills and related behaviours in daily life in normally intelligent adults with TSC and matched controls using the Test of Everyday Attention for Children (TEA-Ch) and the Attention-Deficit Scales for Adults (ADSA). No group differences were demonstrated on selective or sustained attention tasks carried out alone. However, adults with TSC performed significantly worse when these tasks were combined in a cross-modal dual task condition. On the ADSA the TSC group had significantly worse scores on several subscales (attention/concentration, behaviour/disorganization, academic and emotional behaviours) compared to controls and these correlated with dual task performance, indicating a clear impact of dual task deficits on attention-related behaviours in daily life. The presence or absence of epilepsy did not influence dual task performance or attention-deficits in daily life. Taken together with similar findings in children, results suggest that dual task difficulties are a core feature of the neuropsychological phenotype of TSC.