Title: Tabular Deep Learning when $d \gg n$ by Using an Auxiliary Knowledge Graph. Abstract: Machine learning models exhibit strong performance on datasets with abundant labeled samples. However, for tabular datasets with extremely high $d$-dimensional features but limited $n$ samples (i.e. $d \gg n$), machine learning models struggle to achieve strong performance. Here, our key insight is that even in tabular datasets with limited labeled data, input features often represent real-world entities about which there is abundant prior information which can be structured as an auxiliary knowledge graph (KG). For example, in a tabular medical dataset where every input feature is the amount of a gene in a patient's tumor and the label is the patient's survival, there is an auxiliary knowledge graph connecting gene names with drug, disease, and human anatomy nodes. We therefore propose PLATO, a machine learning model for tabular data with $d \gg n$ and an auxiliary KG with input features as nodes. PLATO uses a multilayer perceptron (MLP) to predict the output labels from the tabular data and the auxiliary KG with two methodological components. First, PLATO predicts the parameters in the first layer of the MLP from the auxiliary KG. PLATO thereby reduces the number of trainable parameters in the MLP and integrates auxiliary information about the input features. Second, PLATO predicts different parameters in the first layer of the MLP for every input sample, thereby increasing the MLP’s representational capacity by allowing it to use different prior information for every input sample. Across 10 state-of-the-art baselines and 6 $d \gg n$ datasets, PLATO exceeds or matches the prior state-of-the-art, achieving performance improvements of up to 10.19%. Overall, PLATO uses an auxiliary KG about input features to enable tabular deep learning prediction when $d \gg n$.