In critically ill patients, drug exposure may be influenced by altered drug distribution and clearance. Earlier studies showed that the variability in caspofungin exposure was high in Intensive Care Unit (ICU) patients. The primary objective of this study was to determine if the standard dose of caspofungin resulted in adequate exposure in critically ill patients. A multicenter prospective study in ICU patients with (suspected) invasive candidiasis was conducted in the Netherlands, from November 2013 to October 2015. Patients received standard caspofungin treatment and the exposure was determined on day 3 of treatment. An area under the concentration-time curve over 24 hours (AUC0-24h) of 98 mg*h/L was considered adequate exposure. In case of low exposure (i.e. <79 mg*h/L; ≥20% lower AUC0-24h), the caspofungin dose was increased and the exposure re-evaluated. Twenty patients were included in the study, of which 5 had a positive blood culture. The median caspofungin AUC0-24h at day 3 was 78 mg*h/L (interquartile range (IQR), 69 - 97 mg*h/L). A low AUC0-24h (<79 mg*h/L) was seen in 10 patients. The AUC0-24h was significantly and positively correlated with the caspofungin dose in mg/kg/day (P = 0.011). The median AUC0-24h with a caspofungin dose of 1 mg/kg was estimated using a pharmacokinetic model and was 114.9 mg*h/L (IQR, 103.2 - 143.5 mg*h/L). In conclusion, the caspofungin exposure in ICU patients in this study was low compared with healthy volunteers and other (non-)critically ill patients, most likely due to a larger volume of distribution. A weight-based dose regimen is probably more suitable for patients with substantially altered drug distribution.