Confirmation dialog box then call funtion

Hi There

I have a grid view that contains a Item Template with an ASP Button in.
I would like to have a confirmation dialogue box confirming the delete then call the Function I have written for the delete functionality.

Thanks
Stanton

<asp:GridView ID="gvAllergies" CssClass="grid" runat="server" AutoGenerateColumns="False"
                            CellPadding="4" Width="100%" DataKeyNames="ID" ForeColor="#333333" GridLines="Horizontal"
                            AlternatingRowStyle-BackColor="WhiteSmoke"
                            OnRowCreated="gvAllergies_RowCreated">
                            <FooterStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
                            <Columns>
                            <asp:TemplateField HeaderText="View">
                                <ItemTemplate>
                                    <asp:ImageButton ID="selectAllergy" runat="server" ImageUrl="~/images/Editsml.gif"
                                        OnClick="selectAllergy_Click" CommandArgument='<%# Bind("Id") %>' />
                                </ItemTemplate>
                            </asp:TemplateField>
                                <asp:BoundField DataField="Type" HeaderText="Type" SortExpression="Type" ItemStyle-CssClass="gridrow" />
                                <asp:BoundField DataField="Onset" HeaderText="Onset" SortExpression="Onset" ItemStyle-CssClass="gridrow" />
                                <asp:BoundField DataField="OnCard" HeaderText="On Card" SortExpression="OnCard" ItemStyle-CssClass="gridrow" />
                                <asp:BoundField DataField="OnReport" HeaderText="On Report" SortExpression="OnReport" ItemStyle-CssClass="gridrow" />
                                <asp:BoundField DataField="Confidential" HeaderText="Confidential" SortExpression="Confidential" ItemStyle-CssClass="gridrow" />
                                <asp:TemplateField HeaderText="Delete">
                                 <ItemTemplate>
                                    <asp:ImageButton ID="DeleteAllergy" runat="server" ImageUrl="~/images/Deletesml.gif"
                                        OnClick="DeleteAllergy_Click" CommandArgument='<%# Bind("ID") %>' />
//Onclick Here I would first like a confirmation dialogue the call the delete function.
 
                                </ItemTemplate>
                            </asp:TemplateField>
                            </Columns>
                            <HeaderStyle CssClass="gridhead" />
                            <RowStyle CssClass="gridrow" />
                            <EmptyDataTemplate>
                                <span class="gridrow">There are no current Allergies. Click the button above to add a new Allergy.</span>
                            </EmptyDataTemplate>
                        </asp:GridView>

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